Fix event dispatcher contracts version (#19)

Author: yoanm

composer.json

@@ -35,7 +35,7 @@
     "php": ">=7.1",
     "symfony/config": "^3.0 || ^4.0",
     "symfony/dependency-injection": "^3.0 || ^4.0",
-    "symfony/event-dispatcher-contracts": "^1.0 || ^2.0",
+    "symfony/event-dispatcher-contracts": "^1.0",
     "symfony/http-kernel": "^3.0 || ^4.0",
     "yoanm/jsonrpc-http-server-openapi-doc-sdk": "^0.2",
     "yoanm/jsonrpc-server-doc-sdk": "^0.2",