Add compatibility with symfony 3.* and 4.*

Author: pascal-hofmann

composer.json

@@ -23,8 +23,8 @@
     "require": {
         "php": ">=5.4.0",
         "dflydev/stack-authentication": "1.0.*@dev",
-        "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",