Thanks to Ben Balter and others for pointing out that raw geodata (topojson in this case) can be served from github without cross-domain failure the same way that everything else can be served: under the gh-pages umbrella.
Modified http://d3js.org/d3.v3.min.js to a secure url
Modified http://d3js.org/d3.geo.projection.v0.min.js to a secure url
Modified http://d3js.org/topojson.v0.min.js to a secure url
https://d3js.org/d3.v3.min.js
https://d3js.org/d3.geo.projection.v0.min.js
https://d3js.org/topojson.v0.min.js