Merge pull request #23551 from edx/arch/django22-tox

Django2: Add to tox.ini's envlist

tox.ini

 [tox]
-envlist = py{35,36,37}-django{111,20,21}
+envlist = py{35,36,37}-django{111,20,21,22}
 
 # This is needed to prevent the lms, cms, and openedx packages inside the "Open
 # edX" package (defined in setup.py) from getting installed into site-packages