Simplify conditionalization of mock dependency

Since it is needed only on Python 2.7 and on versions of Python 3 which have reached end of life (before 3.3), move it to the “Python2 only deps” with enum34.

Co-authored-by: (Eliseo) Nathaniel Ruiz Nowell <[email protected]>

Author: musicinmybrain

tox.ini

@@ -36,10 +36,8 @@ deps =
     testing.postgresql
     testing.mysqld
     webtest
-    mock ; python_version < '3.3'
-
     # Python2 only deps
-    py{27}: enum34
+    py{27}: enum34, mock
 
     # pymysql deps
     py{27,34,35}: pymysql < 1.0.0