Remove Travis pin of zope.testrunner; we need at least 4.4.7 in order to run on PyPy3.

.travis.yml

@@ -9,7 +9,7 @@ python:
     - 3.3
     - 3.4
 install:
-    - travis_retry pip install BTrees ZConfig manuel persistent six transaction zc.lockfile zdaemon zope.interface zope.testing zope.testrunner==4.4.4
+    - travis_retry pip install BTrees ZConfig manuel persistent six transaction zc.lockfile zdaemon zope.interface zope.testing zope.testrunner
     - travis_retry pip install -e .
 script:
     - zope-testrunner -u --test-path=src --auto-color --auto-progress