Update zope.testing to current version

The one used before can't be installed any more by current `setuptools` versions because it uses `2to3` which is no longer supported.

buildout.cfg

@@ -7,7 +7,7 @@ versions = versions
 zope.interface = 4.1.3
 zope.exceptions = 4.0.8
 zc.recipe.testrunner = 2.0.0
-zope.testing = 4.5.0
+zope.testing = 4.9
 coverage = 5.1
 
 [py]