Fix invalid escape sequence deprecation warnings
Fix invalid escape sequence deprecation warnings

When running tests with warnings enabled, appear as:

  DeprecationWarning: invalid escape sequence \d

Starting with Python 3.6, invalid escape sequences are deprecated. In a
future Python versions they will be a syntax error. For more details, see:

https://docs.python.org/3/whatsnew/3.6.html#deprecated-python-behavior

> A backslash-character pair that is not a valid escape sequence now
> generates a DeprecationWarning. Although this will eventually become a
> SyntaxError, that will not be for several Python releases.

tomchristie/django-rest-framework,tomchristie/django-rest-framework,jpadilla/django-rest-framework,jpadilla/django-rest-framework,kgeorgy/django-rest-framework,jpadilla/django-rest-framework,kgeorgy/django-rest-framework,tomchristie/django-rest-framework,kgeorgy/django-rest-framework