Reference individual contracts packages

Author: nicolas-grekas

composer.json

@@ -17,7 +17,8 @@
     ],
     "require": {
         "php": "^7.1.3",
-        "symfony/contracts": "^1.1"
+        "symfony/event-dispatcher-contracts": "^1.1",
+        "symfony/service-contracts": "^1.1"
     },
     "require-dev": {
         "psr/container": "^1.0",