Fix URL for WP setup doesn't work as expected

[arturkot]

Steps to reproduce:

1. Run yo chisel.
2. Select "WordPress with Front-end".
3. When "Enter URL" shows up, enter a url different than the default one.
4. When Yo finishes it's job run gulp to fire BrowserSync.
5. It should stuck trying to load localhost:3000.

Looks like alternate URL isn't provided for server.js scripts which results in an error. Manually adding "proxyTarget": "[alternate URL]", inside .yo-rc deals with the issue.