Switch to new Framework :: Zope :: 3 classifier

See zopefoundation/z3c.authviewlet#6 (comment)
for the background behind this.

setup.py

@@ -60,7 +60,7 @@ def read(*rnames):
           'Natural Language :: English',
           'Operating System :: OS Independent',
           'Topic :: Internet :: WWW/HTTP',
-          'Framework :: Zope3'
+          'Framework :: Zope :: 3'
       ],
       url='http://github.com/zopefoundation/zope.app.content',
       license='ZPL 2.1',