Add trove classfier for Wagtail... to Wagtail.

setup.py

@@ -89,6 +89,7 @@ setup(
         'Framework :: Django',
         'Framework :: Django :: 1.11',
         'Framework :: Django :: 2.0',
+        'Framework :: Wagtail',
         'Topic :: Internet :: WWW/HTTP :: Site Management',
     ],
     install_requires=install_requires,