Switch to new Framework :: Zope :: 3 classifier

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

setup.py

@@ -73,7 +73,7 @@ def read(*rnames):
         'Programming Language :: Python :: Implementation',
         'Programming Language :: Python :: Implementation :: CPython',
         'Programming Language :: Python :: Implementation :: PyPy',
-        'Framework :: Zope3',
+        'Framework :: Zope :: 3',
         ],
     packages=find_packages('src'),
     package_dir={'': 'src'},