Update composer.json phantomjs-installer dependency

[sgregson]

composer update fails due to bitbucket cdn issue - since composer.json's phantomjs-installer is pinned to v1.9.8 including bitbucket issues which have since been resolved upstream (jakoch/phantomjs-installer#34). Moving phantomjs-installer v1.9.8 => v2.1.1-p07 permits ENV setup to pull a mirror to work around OAuth issues - I doubt there are breaking changes in the PhantomJS Installer.

Update permits export PHANTOMJS_CDNURL=https://github.com/Medium/phantomjs/; composer update (or similar mirror)

In the interim, modifying the URL scheme in /vendor/jakoch/phantomjs-installer/src/PhantomInstaller/Installer.php to match https://github.com/Medium/phantomjs/archive/v1.9.8/1.9.8-macosx.zip will get you through composer update.