unittest2 is not needed with recent Python versions.

--- passlib-1.7.4/tox.ini.orig
+++ passlib-1.7.4/tox.ini
@@ -149,7 +149,6 @@
     # common
     nose
     coverage
-    unittest2
 
     # totp helper tests
     # NOTE: cryptography requires python-dev, libffi-dev, libssl-dev