Bump gevent to 1.3.6
Bump gevent to 1.3.6

Now that gevent has included a fix for
https://github.com/gevent/gevent/issues/1260 in a release we should bump to it
so that we don't have to manually recompile gevent whenever we use python 3.7

[ci integration]

hackaugusto/raiden,hackaugusto/raiden