version-bump django-modelcluster to 2.0

setup.py

@@ -22,7 +22,7 @@ except ImportError:
 
 install_requires = [
     "Django>=1.8.1,<1.10",
-    "django-modelcluster>=1.1,<1.2",
+    "django-modelcluster>=2.0,<3.0",
     "django-taggit>=0.18,<0.19",
     "django-treebeard>=3.0,<5.0",
     "djangorestframework>=3.1.3",