Issue DeprecationWarning when running on Python 2

Author: atodorov

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Version 0.8.0 (unreleased)
 
+* This is the last version to support Python 2. Issues a deprecation warning!
 * [#109](http://github.com/landscapeio/pylint-django/pull/109),
   adding 'urlpatterns', 'register', 'app_name' to good names. Obsoletes
   [#111](http://github.com/landscapeio/pylint-django/pull/111), fixes

pylint_django/__init__.py

@@ -1,5 +1,13 @@
 """pylint_django module."""
 from __future__ import absolute_import
+
+import sys
+import warnings
+
 from pylint_django import plugin
 
+if sys.version_info < (3, ):
+    warnings.warn("Version 0.8.0 is the last to support Python 2. "
+                  "Please migrate to Python 3!", DeprecationWarning)
+
 register = plugin.register