fix: never proxy hot-reload websocket requests

[ajhyndman]

• [x] This is a bugfix
• [ ] This is a feature
• [ ] This is a code refactor
• [ ] This is a test update
• [ ] This is a docs update
• [ ] This is a metadata update

For Bugs and Features; did you add new tests?

Please let me know what kind of test could be appropriate for this change.

Motivation / Use-Case

Both create-react-app and vue-cli-service have introduced workarounds for this, but it seems to me that this is always desirable behaviour for webpack-dev-server.

https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb https://github.com/facebook/create-react-app/pull/7444

[linux-foundation-easycla[bot]]

The committers are authorized under a signed CLA.

• :white_check_mark: Andrew Hyndman (251a52fef6f3e62c0c10e350f54a87eddaf073d2)