Fixed win10 cannot handle EventSource Response

[max918]

This PR contains a:

• [x] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [ ] typo fix
• [ ] metadata update

Motivation / Use-Case

on Window 10, browsers would not process (or cannot handle) the EventSource's HTTP response if the response is without 'Content-Length'. It cause the client.js cannot be notified to update frontend changes.

But hot-middleware is using the streaming data approach to achieve eventsource. So, adding the Response Header 'Content-Length: -1' can solve the problem.

The fix is already tested on Chrome browser of window 10 (64 bit) and Mac OS.

https://github.com/webpack-contrib/webpack-hot-middleware/issues/101

Breaking Changes

Additional Info

[jsf-clabot]

All committers have signed the CLA.

[alexander-akait]

Can you create minimum reproducible test repo, adding this header is breaking change and break logic for other types