Add compatibility with symfony 3.* and 4.*

Author: pascal-hofmann

composer.json

@@ -22,8 +22,8 @@
     },
     "require": {
         "php": ">=5.4.0",
-        "symfony/http-foundation": "~2.1",
-        "symfony/http-kernel": "~2.1"
+        "symfony/http-foundation": "~2.1|~3.0|~4.0",
+        "symfony/http-kernel": "~2.1|~3.0|~4.0"
     },
     "require-dev": {
         "phpunit/phpunit": "3.7.21",