feat: Support for 3.x (fix #7)

Author: leeqvip

composer.json

@@ -10,11 +10,11 @@
     ],
     "license": "Apache-2.0",
     "require": {
-        "casbin/casbin": "^2.0",
+        "casbin/casbin": "^3.0",
         "techone/database": "^0.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "~7.0",
+        "phpunit/phpunit": "~7.0|~8.0|~9.0",
         "php-coveralls/php-coveralls": "^2.1"
     },
     "autoload": {