Reference individual contracts packages

Author: nicolas-grekas

composer.json

@@ -17,9 +17,9 @@
     ],
     "require": {
         "php": "^7.1.3",
-        "symfony/contracts": "^1.1",
         "symfony/polyfill-mbstring": "~1.0",
-        "symfony/polyfill-php73": "^1.8"
+        "symfony/polyfill-php73": "^1.8",
+        "symfony/service-contracts": "^1.1"
     },
     "require-dev": {
         "symfony/config": "~3.4|~4.0",