chore(test): Add test coverage Py39 Py3-10 #7

Test coverage for the last 2 releases of Python was not implemented.

closes #7

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py36, py37,py38 pypy, docs
+envlist = py36, py37,py38, py39, py3.10 pypy, docs
 skipsdist = true
 
 [travis]
@@ -10,7 +10,7 @@ python =
 
 [testenv:docs]
 basepython=python
-changedir=docs
+changedir=docs/source
 deps=sphinx
 commands=
     sphinx-build -b html -d {envtmpdir}/doctrees . {envtmpdir}/html