bug #6482 fixed wrong secret string in array examples (OskarStark)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #6482).

Discussion
----------

fixed wrong secret string in array examples

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7+
| Fixed tickets | --

Looks like this is a copy paste error from older doc versions where the string `$ecret` was used.

This needs to be applied to all branches from 2.7 on

Check the old version of the docs here where the `$ecret` string is used:
http://symfony.com/doc/2.6/cookbook/bundles/configuration.html

Commits
-------

f7950ab fixed wrong secret string in array examples

Author: wouterj

cookbook/bundles/configuration.rst

@@ -139,7 +139,7 @@ For the configuration example in the previous section, the array passed to your
         array(
             'twitter' => array(
                 'client_id' => 123,
-                'client_secret' => '$secret',
+                'client_secret' => 'your_secret',
             ),
         ),
     )
@@ -155,7 +155,7 @@ beneath it, the incoming array might look like this::
         array(
             'twitter' => array(
                 'client_id' => 123,
-                'client_secret' => '$secret',
+                'client_secret' => 'your_secret',
             ),
         ),
         // values from config_dev.yml