Update doctrine.rst

reference/configuration/doctrine.rst

@@ -364,7 +364,7 @@ The following block shows all possible configuration keys:
     version).
 
     If you are running a MariaDB database, you should prefix the ``server_version`` 
-    with ``mariadb-`` (ex: ``server_version: mariadb-10.2.12``).
+    with ``mariadb-`` (e.g. ``server_version: mariadb-10.2.12``).
 
     Always wrap the server version number with quotes to parse it as a string
     instead of a float number. Otherwise, the floating-point representation