Including coverage in test dependencies

Author: Carl Crowder

setup.py

@@ -22,7 +22,7 @@
     ],
     extras_require={
         'with_django': ['Django'],
-        'for_tests': ['django_tables2', 'factory-boy'],
+        'for_tests': ['django_tables2', 'factory-boy', 'coverage'],
     },
     license='GPLv2',
     classifiers=[