Composer: add minimum php version of 7

Author: sirbrillig

composer.json

@@ -19,7 +19,9 @@
     "scripts": {
         "test": "./vendor/bin/phpunit"
     },
-    "require": {},
+    "require" : {
+        "php" : "^7.0"
+    },
     "require-dev": {
         "sirbrillig/phpcs-variable-analysis": "^2.0.1",
         "dealerdirect/phpcodesniffer-composer-installer": "^0.4.4",