Fix doc for 2.6+, server:start replace ...:run

Author: Kevinrob

cookbook/web_server/built_in.rst

@@ -37,7 +37,7 @@ can change the socket passing an IP address and a port as a command-line argumen
 
 .. code-block:: bash
 
-    $ php app/console server:run 192.168.0.1:8080
+    $ php app/console server:start 192.168.0.1:8080
 
 .. note::