TODO: redo just using d3.interpolateZoom, duh.
Modified //cdn.rawgit.com/gka/d3-jetpack/master/d3-jetpack.js to a secure url
https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js
https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js
https://cdn.rawgit.com/gka/d3-jetpack/master/d3-jetpack.js