Update code block in quickstart-app-plugin tutorial to use named import.

Signed-off-by: Brent Sharrow <bsharrow4@gmail.com>

docs/tutorials/quickstart-app-plugin.md

@@ -146,11 +146,9 @@ import {
 } from '@backstage/core';
 import { graphql } from '@octokit/graphql';
 
-const ExampleFetchComponent = () => {
+export const ExampleFetchComponent = () => {
   return <div>Nothing to see yet</div>;
 };
-
-export default ExampleFetchComponent;
 ```
 
 3. Save that and ensure you see no errors. Comment out the unused imports if