我正在运行以下代码：
sudo add-apt-repository -y ppa:ethereum/ethereum
错误信息是：
...
Reading package lists... Done
E: The method driver /usr/lib/apt/methods/hpttps could not be found.
N: Is the package apt-transport-hpttps installed?
E: Some index files failed to download. They have been ignored, or old ones used instead.
我怎样才能解决这个问题？