Use ">=" for the "php" requirement

Author: nicolas-grekas

composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": "^7.1.3",
+        "php": ">=7.1.3",
         "ext-xml": "*",
         "symfony/cache": "^4.4|^5.0",
         "symfony/config": "^4.3.4|^5.0",