Allow symfony/class-loader 3.0 to be installed

composer.json

@@ -13,7 +13,7 @@
     ],
     "require": {
         "php": ">=5.3.2",
-        "symfony/event-dispatcher": "~2.3"
+        "symfony/event-dispatcher": "~2.3|~3.0"
     },
     "require-dev": {
         "phpunit/phpunit": "~3.7",