Switch to new Framework :: Zope :: 3 classifier

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

setup.py

@@ -76,7 +76,7 @@ def read(*rnames):
           'Operating System :: OS Independent',
           'Topic :: Internet :: WWW/HTTP',
           'Topic :: Communications :: Email',
-          'Framework :: Zope3',
+          'Framework :: Zope :: 3',
       ],
       packages=find_packages('src'),
       package_dir={'': 'src'},