我已经使用 rvm 安装了 jruby-1.7.16，并且 java open jdk 版本为 1.7.0_75。
bundle install 成功，以下是我运行 bundle exec rake db:migrate --trace 时出现的错误
test@pts00433-vm8:~/Travis/travis-logs$ bundle exec rake db:migrate --trace
Jdbc-Postgres is only for use with JRuby
** Invoke db:migrate (first_time)
** Execute db:migrate
rake aborted!
Sequel::AdapterNotFound: LoadError: cannot load such file -- java
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/adapters/jdbc.rb:1:in `require'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/adapters/jdbc.rb:1:in `<top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:29:in `require'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:29:in `adapter_class'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:52:in `connect'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/core.rb:95:in `connect'
/home/test/Travis/travis-logs/lib/travis/logs/helpers/database.rb:18:in `create_sequel'
/home/test/Travis/travis-logs/Rakefile:14:in `block (2 levels) in <top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `call'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `block in execute'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `each'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `execute'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/usr/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/bin/rake:33:in `<top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/bin/rake:23:in `load'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/bin/rake:23:in `<main>'
LoadError: cannot load such file -- java
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/adapters/jdbc.rb:1:in `require'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/adapters/jdbc.rb:1:in `<top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:29:in `require'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:29:in `adapter_class'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/database/connecting.rb:52:in `connect'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/sequel-4.0.0/lib/sequel/core.rb:95:in `connect'
/home/test/Travis/travis-logs/lib/travis/logs/helpers/database.rb:18:in `create_sequel'
/home/test/Travis/travis-logs/Rakefile:14:in `block (2 levels) in <top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `call'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:240:in `block in execute'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `each'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:235:in `execute'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/usr/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/task.rb:165:in `invoke'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:150:in `invoke_task'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block (2 levels) in top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `each'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:106:in `block in top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:115:in `run_with_threads'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:100:in `top_level'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:78:in `block in run'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:176:in `standard_exception_handling'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/lib/rake/application.rb:75:in `run'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/gems/rake-10.4.2/bin/rake:33:in `<top (required)>'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/bin/rake:23:in `load'
/home/test/Travis/travis-logs/vendor/bundle/ruby/2.1.0/bin/rake:23:in `<main>'
Tasks: TOP => db:migrate