Enhance pypy support

[Rémi Alvergnat]

Thanks for this plugin.

It works nicely with CPython, but pypy support doesn't solves to latest version.

pyenv latest install pypy
Latest version is 'pypy-stm-2.5.1'

But it should gives pypy-5.7.1

[Rémi Alvergnat]

ping @momo-lab

[momo-lab]

#3 is merged.
#5 is checking now. plz wait.