travis-ci: now use pypy3.5-5.8.0 instead of pypy3
travis-ci: now use pypy3.5-5.8.0 instead of pypy3

I have changed travis.yml to use `pypy3.5-5.8.0` instead of `pypy3`.
Travis uses an outdated version of `pypy3`.
`pypy3.5-5.8.0` contains some fixes for multithreaded scripts, which *may* fix the bug in the travic-ci build for `neat.threaded.ThreadedEvaluator`.
drallensmith/neat-python,CodeReclaimers/neat-python