Correct a mistaken path in the "Advanced Configuration" documentation

Summary: Ref PHI2071. This path is incorrect; the correct path is `local.json`.

Test Plan: Looked in my `conf/local/` directory.

Differential Revision: https://secure.phabricator.com/D21663

Author: epriestley

src/docs/user/configuration/advanced_configuration.diviner

@@ -21,7 +21,7 @@ to lowest priority:
   - **Database**: Values are stored in the database and edited from the web UI
     by administrators. They have the highest priority and override other
     settings.
-  - **Local**: Values are stored in `conf/local/config.json` and edited by
+  - **Local**: Values are stored in `conf/local/local.json` and edited by
     running `bin/config`.
   - **Config Files**: Values are stored in a config file in `conf/`. The file
     to use is selected by writing to `conf/local/ENVIRONMENT`, or setting the