minor #4026 Updating Symfony version from 2.4 to 2.5 (danielsan)

This PR was merged into the 2.5 branch.

Discussion
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Updating Symfony version from 2.4 to 2.5

The descriptions are still displaying the old version

Commits
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81d962f Configuring composer.json to use the 2.5 version
2299df0 Updating Symfony version from 2.4 to 2.5

book/from_flat_php_to_symfony2.rst

@@ -431,7 +431,7 @@ content:
 
     {
         "require": {
-            "symfony/symfony": "2.4.*"
+            "symfony/symfony": "2.5.*"
         },
         "autoload": {
             "files": ["model.php","controllers.php"]