Add the version 4 of symfony in composer.json

Author: Julien Grelet

composer.json

@@ -94,7 +94,7 @@
 
     "require": {
         "php":                          ">=5.3.3",
-        "symfony/framework-bundle":     "~2.3|~3.0",
+        "symfony/framework-bundle":     "~2.3|~3.0|~4.0",
         "symfony/security-bundle":      "~2.3|~3.0",
         "symfony/options-resolver":     "~2.3|~3.0",
         "symfony/form":                 "~2.3|~3.0",