Ajoute des contraintes de version de PHP.

composer.json

@@ -10,6 +10,7 @@
         }
     ],
     "require": {
+        "php": "^5.6 || ^7.0 || ^8.0",
         "irstea/composer-require-checker-shim": "@stable",
         "irstea/pcov-clobber-plugin": "@stable",
         "irstea/php-cs-fixer-config": "@stable",