refactor: Exceptions must use `as`

- And now the single "except" does
Signed-off-by: David Haynes <dhaynes3@gmu.edu>

whats_open/whats_open/settings/production.py

@@ -15,7 +15,7 @@ def get_env_setting(setting):
     """ Get the environment setting or return exception """
     try:
         return environ[setting]
-    except KeyError:
+    except KeyError as ex:
         error_msg = "Set the %s env variable" % setting
         raise ImproperlyConfigured(error_msg)