Fixed a url to the contributing guide in a code comment.

# NAME and potentially authentication information. See the

# following section in the docs for more information:

#

# http://docs.djangoproject.com/en/dev/internals/contributing/#unit-tests

# https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/

#

# The different databases that Django supports behave differently in certain

# situations, so it is recommended to run the test suite against as many