fix: Append startURL to the initial url loaded

[jcesarmobile]

When using a custom scheme (app in example), the initial url loaded is app://localhost

This PR makes the initial url loaded to append the startURL to the url, in example app://localhost/index.html

This makes possible to run the tests as they use <content src="cdvtests/index.html" />, so now the url loaded will be app://localhost/cdvtests/index.html instead of app://localhost.

[erisu]

👍 LGTM

Tested locally both with and without paramedic.

Waiting for @dpogue to review and merge since he will be preparing the upcoming patch release.

[dpogue]

Looks good to me