Use ">=" for the "php" requirement

Author: nicolas-grekas

composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": "^7.1.3",
+        "php": ">=7.1.3",
         "doctrine/event-manager": "~1.0",
         "doctrine/persistence": "^1.3",
         "symfony/polyfill-ctype": "~1.8",