Bump edx-enterprise to 0.55.1.

This updates edx-enterprise to 0.55.1 to include changes related to
enteprise tracking events.

requirements/edx/base.txt

@@ -47,7 +47,7 @@ edx-lint==0.4.3
 astroid==1.3.8
 edx-django-oauth2-provider==1.2.5
 edx-django-sites-extensions==2.3.0
-edx-enterprise==0.55.0
+edx-enterprise==0.55.1
 edx-oauth2-provider==1.2.2
 edx-opaque-keys==0.4.0
 edx-organizations==0.4.8