Fix asset path in asset fingeprinter

The asset fingerprinter was hard coded to always point to `/static`.

It needs to change depending on which environment the app is running
in.

app/__init__.py

@@ -103,6 +103,7 @@ def create_app(application):
     notify_environment = os.environ['NOTIFY_ENVIRONMENT']
 
     application.config.from_object(configs[notify_environment])
+    asset_fingerprinter._asset_root = application.config['ASSET_PATH']
 
     init_app(application)
     antivirus_client.init_app(application)

app/config.py

@@ -113,6 +113,7 @@ class Test(Development):
     ANTIVIRUS_API_KEY = 'test-antivirus-secret'
 
     ASSET_DOMAIN = 'static.example.com'
+    ASSET_PATH = 'https://static.example.com/'
 
 
 class Preview(Config):