chore(composer): set min php 7, add test script

Author: adhocore

composer.json

@@ -3,7 +3,7 @@
     "description": "Ultra lightweight JSON web token (JWT) library for PHP5.5+.",
     "type": "library",
     "keywords": [
-        "jwt", "jwt-php", "auth", "json-web-token", "token"
+        "jwt", "jwt-php", "auth", "json-web-token", "token", "jwt-auth"
     ],
     "license": "MIT",
     "authors": [
@@ -23,9 +23,12 @@
         }
     },
     "require": {
-        "php": ">=5.5"
+        "php": ">=7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8 || ^5.7 || ^6.5"
+        "phpunit/phpunit": "^6.5 || ^7.5"
+    },
+    "scripts": {
+        "test": "vendor/bin/phpunit"
     }
 }