Incorrect url rewrites when "homepage" parameter is set

[immanuel-h]

Hi,

Steps to reproduce

1. set "homepage" in package.json to /fresco
2. npm run build (even outputs correctly "The project was built assuming it is hosted at /fresco/")
3. host the generated package somehow under /fresco (eg. simply in nginx)
4. go to your page

Expected: url rewritten to http://[yoursite]/fresco/styles/add/scratch

Actual: url rewritten to http://[yoursite]/styles/add/scratch

This is not a concern as long as the user does not reload the page, but once they do it actually breaks stuff.