Confirm python 3.8 support

[Jeffrey McLarty]

• update travis
• update docs

[Bruk Habtu]

(venv) bruk:pyenvdiff-lib/ (master✗) $ which pytest                  [14:07:57]
/Users/bruk/Documents/pyenvdiff-lib/venv/bin/pytest
(venv) bruk:pyenvdiff-lib/ (master✗) $ pytest tests                  [14:08:04]
============================= test session starts ==============================
platform darwin -- Python 3.8.0a0, pytest-3.0.5, py-1.7.0, pluggy-0.4.0
rootdir: /Users/bruk/Documents/pyenvdiff-lib, inifile:
collected 89 items

tests/test_pyenvdiff.py .........................................................................................

========================== 89 passed in 1.29 seconds ===========================
(venv) bruk:pyenvdiff-lib/ (master✗) $ which python                  [14:08:10]
/Users/bruk/Documents/pyenvdiff-lib/venv/bin/python
(venv) bruk:pyenvdiff-lib/ (master✗) $ python                        [14:08:13]
Python 3.8.0a0 (heads/master:a9655b7, Nov 12 2018, 13:48:09)
[Clang 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

Tests are green on Python3.8-dev

[Jeffrey McLarty]

w00t! Thanks for the help, soooo much! This is great!

[Jeffrey McLarty]

Need to add tags to setup.py and probably search, say, "3.6" see where else we might need to add 3.7 or 3.8