Dev server is trying to proxy a CSS file in public dir

[GAumala]

Is this a bug report?

Yes

Environment

node: v10.0.0
yarn: 1.6.0
create-elm-app: 1.10.4

OS: Arch Linux

Steps to Reproduce

1. Set a proxy in elm-package.json
2. Add a single stylesheet to public, something like public/style.css
3. Link to that stylesheet in public/index.html with <link rel="stylesheet" href="%PUBLIC_URL%/style.css">
4. Run elm-app start

Expected Behavior

I expected the requests to files in public to not be proxied, and the dev server should serve those files without any extra configuration.

Actual Behavior

The stylesheet is not served because the request to the stylesheet in public is being proxied every single time.

Reproducible Demo

(Paste the link to an example project and exact instructions to reproduce the issue.)

[halfzebra]

Should be fixed in #284

Please let me know if this is still a problem.