Let's attempt to use the matrix more and/or pray newer Sphinx works on pypy3

Author: bitprophet

.travis.yml

@@ -47,7 +47,7 @@ script:
   # We have no real tests at present so we just make sure installation works,
   # first off.
   - pip install .
-  # Websites build OK? (Not on PyPy3, Sphinx is all "who the hell are you?" =/
-  - "if [[ $TRAVIS_PYTHON_VERSION != 'pypy3' ]]; then inv docs; fi"
+  # Does our own dogfooding website build ok? :D
+  - inv docs
   # I have this in my git pre-push hook, but contributors probably don't
   - flake8