Update pytz to 2015.2

pytz changed their versioning scheme from using letters to using
numbers. The old scheme is screwing up new versions of pip.

docs/shared/requirements.txt

@@ -51,7 +51,7 @@ pygments==1.5
 pymongo==2.4.1
 python-memcached==1.48
 python-openid==2.2.5
-pytz==2012h
+pytz==2015.2
 PyYAML==3.10
 requests==2.3.0
 Shapely==1.2.16

requirements/edx/base.txt

@@ -69,7 +69,7 @@ python-memcached==1.48
 python-openid==2.2.5
 python-dateutil==2.1
 python-social-auth==0.1.23
-pytz==2012h
+pytz==2015.2
 pysrt==0.4.7
 PyYAML==3.10
 requests==2.3.0