Try to install Django only

Signed-off-by: Michal Čihař <michal@cihar.com>

.scrutinizer.yml

@@ -11,7 +11,7 @@ filter:
         - '*/test/*'
         - '*/migrations/*'
 before_commands:
-    - pip install -r requirements.txt
+    - pip install Django
 build:
     environment:
         python: "3.5.0"