The Tobler world-in-a-square projection is the d3.geo.cylindricalEqualArea
projection with a parallel of 55° 39ʹ 14.2812ʺ. It is available in the geo.projection D3 plugin.
Changed /mbostock/raw/4090846/world-50m.json to a local referenece
https://d3js.org/d3.v3.min.js
https://d3js.org/d3.geo.projection.v0.min.js
https://d3js.org/topojson.v1.min.js