chore(ci): Remove PHANTOMJS_CDNURL, nit
chore(ci): Remove PHANTOMJS_CDNURL, nit

Seems like PHANTOMJS_CDNURL is not needed anymore now that PhantomJS support is [depracated](https://github.com/mochajs/mocha/blob/6a796cbbcd6c9f805e482c424327c82ed0398dbf/CHANGELOG.md#compatibility).

Please ignore if I am wrong.
boneskull/mocha,boneskull/mocha,igwejk/mocha,adamgruber/mocha,outsideris/mocha,adamgruber/mocha,outsideris/mocha,mochajs/mocha,igwejk/mocha,mochajs/mocha,mochajs/mocha,adamgruber/mocha,boneskull/mocha