Add default to export for Service Binding example. This is required to make the code sample work. (#18163)

Partially addresses issue #17421.

Signed-off-by: Rob Sutter <[email protected]>

Author: rts-rob

src/content/docs/workers/runtime-apis/bindings/service-bindings/index.mdx

@@ -60,7 +60,7 @@ main = "./src/workerB.js"
 ```js
 import { WorkerEntrypoint } from "cloudflare:workers";
 
-export class WorkerB extends WorkerEntrypoint {
+export default class WorkerB extends WorkerEntrypoint {
   // Currently, entrypoints without a named handler are not supported
   async fetch() { return new Response(null, {status: 404}); }