Fix: Codeblock Syntax Highlighting (#23545)

I don't believe NodeJS code should receive Bash syntax highlighting :).



## Bug

- [x] Related issues linked using `fixes #number`
- [] Integration tests added

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.

## Documentation / Examples

- [ ] Make sure the linting passes

examples/custom-server-express/README.md

@@ -28,11 +28,11 @@ npm install body-parser
 
 Use the package within server.js:
 
-```bash
-const bodyParser = require('body-parser');
+```js
+const bodyParser = require('body-parser')
 
 app.prepare().then(() => {
-  const server = express();
+  const server = express()
   server.use(bodyParser.urlencoded({ extended: true }))
   server.use(bodyParser.json())
 })