Fix typo in setup.cfg

Fixes PyPI error:

    HTTPError: 400 Client Error: Invalid value for classifiers. Error:
    Classifier '[' is not a valid classifier. for url:
    https://upload.pypi.org/legacy/

setup.cfg

@@ -7,7 +7,7 @@ author_email = [email protected]
 description = Full featured redis cache backend for Django.
 long_description = file: README.rst
 license = BSD-3-Clause
-classifiers = [
+classifiers =
     Development Status :: 5 - Production/Stable
     Environment :: Web Environment
     Framework :: Django