fix asset paths when wordpress is hosted from an apache user directory

$_SERVER['HTTP_HOST'] was returning `localhost` instead of `localhost/~jon/bedrock` which breaking css and script asset paths in the roots theme.

This did not appear to be a problem with other wordpress themes (at least the built in ones), so this fix can be disregarded if the roots theme is updated to play nicely with apache user directories.  I figured since we are setting `WP_HOME` in the `.env` file already, it was easier to just utilize it.