feat: use koa

Author: ruanyf

package.json

@@ -4,7 +4,7 @@
   "description": "An example of oAuth2.0 using node",
   "main": "index.js",
   "repository": "https://githubb.com/ruanyf/node-oauth-demo",
-  "author": "sohamkamani",
+  "author": "Ruan Yifeng",
   "license": "MIT",
   "dependencies": {
     "axios": "^0.18.0",