Much better fix for #479 using tox

Author: kotfu

tests/test_docs.py

@@ -9,6 +9,12 @@ passenv = CI TRAVIS TRAVIS_* APPVEYOR*
 setenv =
     PYTHONPATH={toxinidir}
 
+[testenv:docs]
+basepython = python3.7
+changedir = docs
+extras = dev
+commands = sphinx-build -b html -d {envtmpdir}/doctrees . {envtmpdir}/html
+
 [testenv:py34]
 deps =
   codecov