Make docs url fetcher support multiple sources but not old Djangos
Make docs url fetcher support multiple sources but not old Djangos

The djangoproject site no longer hosts docs for versions before 1.7, so
we shouldn't generate urls for these versions.

Readthedocs still has them but in a slightly different format, so if we
really wanted to still link to them we probably could.

refreshoxford/django-cbv-inspector,refreshoxford/django-cbv-inspector,refreshoxford/django-cbv-inspector,refreshoxford/django-cbv-inspector