Update koa to v3

Author: RichDom2185

package.json

@@ -16,7 +16,7 @@
   "dependencies": {
     "@koa/cors": "^5.0.0",
     "@teamwork/websocket-json-stream": "^2.0.0",
-    "koa": "^2.16.1",
+    "koa": "^3.0.1",
     "koa-bodyparser": "^4.4.1",
     "koa-easy-ws": "^2.1.0",
     "sharedb": "^5.1.1",