the documentation of 'neat.parallel.ParallelEvolver' said that
'eval_function' should take one argument (the genome), but it is
called with two arguments(the genome and the config).

I have added a test for neat.threaded.ThreadedEvaluator based on the
test for neat.parallel.ParallelEvaluator.

i removed the test for checki if
'neat.threaded.ThreadedEvaluator.__del__'  stops the threads. This is
because __del__ is not always called and thus may result in false test
results.

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Travis uses an outdated version of `pypy3`.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`.

travis-ci: explicitly set pypy3 version to `pypy3.5-5.8.0`

travis-ci uses an outdated `pypy3`, which contains a bug when using multiple threads. This causes some test to fail on `pypy3`.
Replacing `pypy3` with `pypy3.5-5.8.0` in `.travis.yml` fixes the tests.

I also added another test for general functionality of `neat.threaded.ThreadedEvaluator`.