enable configuration of allowed host

Author: tardyp

README.rst

@@ -160,6 +160,9 @@ for this purpose::
 
     SECRET_KEY=$(python -c "from django.core.management import utils; print(utils.get_random_secret_key())")
 
+You will also need to setup the VC_ALLOWED_HOSTS environment variable to match the hostname where the app is deployed::
+
+    VC_ALLOWED_HOSTS=vulnerablecode.your.domain.example.com
 
 Using Nix
 ~~~~~~~~~

vulnerablecode/settings.py

@@ -28,7 +28,7 @@
 DEBUG = False
 
 ALLOWED_HOSTS = [
-    ".herokuapp.com",
+    os.environ.get("VC_ALLOWED_HOSTS", ".herokuapp.com"),
 ]
 
 # Application definition