我发现pgfplots包已安装但出现此错误：unknown key
如果可以，我该如何添加该包？
Package pgfkeys Error: Choice '1.8' unknown in key '/pgfplots/compat/anchors'. I am going to ignore this key. \pgfplotsset{compat=1.8}
我找不到文件pgflibrarypgfplots.fillbetween.code.tex。\usepgfplotslibrary{fillbetween}