Update league/oauth2-server to ^8.0.0

Author: Tsvetomir Lazarov

composer.json

@@ -22,7 +22,7 @@
     },
     "require": {
         "php": "^7.1",
-        "league/oauth2-server": "^7.3.0",
+        "league/oauth2-server": "^8.0.0",
         "psr/container": "^1.0",
         "psr/http-message": "^1.0.1",
         "psr/http-server-middleware": "^1.0",