fix(deps): update dependency koa to v3 [security]

Author: renovate[bot]

plugin-serve/package.json

@@ -43,7 +43,7 @@
     "prepack": "pkgbld-internal prune"
   },
   "dependencies": {
-    "koa": "^2.14.1",
+    "koa": "^3.0.0",
     "koa-static": "^5.0.0",
     "koa-logger": "^3.2.1",
     "@niceties/logger": "^1.1.4",