Update 2019-04-15-gl-config.md

Author: farhatahmad

_posts/2019-04-15-gl-config.md

@@ -17,7 +17,7 @@ By default Greenlight is deployed to the `/b` sub directory. If you are running
 
 If you with to use a relative root other than `/b`, you can do the following:
 
-1. Change the `RELATIVE_ROOT_URL` environment variable.
+1. Change the `RELATIVE_URL_ROOT` environment variable.
 1. Update the `/etc/bigbluebutton/nginx/greenlight.nginx` file to reflect the new relative root.
 1. Restart Nginx and the Greenlight server.