Apparently 3.6 is not available in the travis image anymore, this PR sets it to 3.6.7. Using a patch version probably means that this will break again soon, but I don't see how to fix it right now.
$ pyenv versions
system
2.7.15
* 3.6.7 (set by PYENV_VERSION environment variable)
3.7
3.7.1
Fix #69.
Apparently
3.6
is not available in the travis image anymore, this PR sets it to3.6.7
. Using a patch version probably means that this will break again soon, but I don't see how to fix it right now.