chore(deps): bump @koa/router from 14.0.0 to 15.0.0 in /examples/custom-receiver (#2733)

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

examples/custom-receiver/package.json

@@ -11,7 +11,7 @@
   },
   "license": "MIT",
   "dependencies": {
-    "@koa/router": "^14",
+    "@koa/router": "^15",
     "@slack/bolt": "^4",
     "@slack/logger": "^4.0.0",
     "@slack/oauth": "^3",