Do not include target url when setting commit status to 'error'

[zpnk]

See here and here.

The url will usually result in a 404 from now.sh anyway since the deploy failed. Including it can be confusing if the user tries to click on it to find out what the error was.

[jimthedev]

This also plays into #14 / #8 since at the moment if you happened an existing deploy with the same then you would not see a 404 and instead would see the first deploy.