docs: change deprecated fallback url
Closes
@@ -141,7 +141,7 @@ Let's dive into the various settings:
that URL in the next sections.
Note: In this example we did not define a value for the optional setting
-`OAUTH2_ERROR_URL`. This URL can be used to provide an endpoint which will
+`URLS_ERROR`. This URL can be used to provide an endpoint which will
receive error messages from ORY Hydra that should be displayed to the end user.
The URL receives `error` and `error_description` parameters. If this value is
not set, Hydra uses the fallback endpoint `/oauth2/fallbacks/error` and displays
