Development mode serves HTML in response to /env.js

[x2048]

This can be reproduced with the example in sample/v2.

• Upgrade to react-scripts 5.0.1
• npm install && npm start
• Inspect the env.js request with the network tab - response will be a chunk of HTML, causing error message in the console.

Possible solution:

• Placing an empty public/env.js avoids the problem.