Fix PyPy unit test failure

[Mat001]

Summary

• Fixing unit tests failing on PyPy/PyPy3
• bumped mmh3 library version to 3.0.0 as that helped eliminate some failures when testing locally

[coveralls]

Coverage remained the same at 95.883% when pulling 8b11e23 on mpirnovar/fix_pypy into 5fefd2b on master.

[aliabbasrizvi]

Seems like a risky change given dropped support for Python 2.7, 3.3, 3.4: https://github.com/hajimes/mmh3/blob/master/README.md

[Mat001]

Seems like a risky change given dropped support for Python 2.7, 3.3, 3.4: https://github.com/hajimes/mmh3/blob/master/README.md

Good to see you, Ali!
Well, PyPy / PyPy3 unit tests have been failing because of mmh3.
Will not be rushing into breaking stuff for sure. Investigating atm ..

[Mat001]

Addressed in #318 - note that failing dependency installations can be seen when expanding the view in TravisCI log console. A small triangle icon to the left of pip install -r requirements.txt...

Also debating if worth downgrading cryptography lib (which caused filures) because that will cause other py versions tests to fail in the future. MAybe better to make a note in README for pypy/pypy3 to require a diff cryptography version