[FrameworkBundle] Fix form conflict rule

Author: Robin Chalas

composer.json

@@ -65,7 +65,7 @@
         "phpunit/phpunit": "<4.8.35|<5.4.3,>=5.0",
         "symfony/asset": "<3.3",
         "symfony/console": "<3.4",
-        "symfony/form": "<3.3",
+        "symfony/form": "<3.4",
         "symfony/property-info": "<3.3",
         "symfony/serializer": "<3.3",
         "symfony/translation": "<3.4",