Merge branch '3.3' into 3.4

* 3.3:
  Removed useless argument $definition
  Fix comment
  [Config] Fix checking class existence freshness
  bumped Symfony version to 3.3.7
  updated VERSION for 3.3.6
  updated CHANGELOG for 3.3.6
  Bump minimal PHP version to ^5.5.9|>=7.0.8

Author: nicolas-grekas

composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": ">=5.5.9",
+        "php": "^5.5.9|>=7.0.8",
         "symfony/polyfill-mbstring": "~1.0"
     },
     "require-dev": {