minor #5852 Fix doc for 2.6+, server:start replace ...:run (Kevinrob)

This PR was submitted for the 2.6 branch but it was merged into the 2.7 branch instead (closes #5852).

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

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.6
| Fixed tickets | -

Commits
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14d1577 Fix doc for 2.6+, `server:start` replace `...:run`

Author: xabbuh

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::