[EventDispatcher] dont allow event-dispatcher-contracts ^2

Author: nicolas-grekas

composer.json

@@ -17,7 +17,7 @@
     ],
     "require": {
         "php": "^7.1.3",
-        "symfony/event-dispatcher-contracts": "^1.1|^2"
+        "symfony/event-dispatcher-contracts": "^1.1"
     },
     "require-dev": {
         "symfony/dependency-injection": "^3.4|^4.0|^5.0",