this iteration uses d3 version 4
the changes to update from d3v3 to d3v4 were pretty straightforward - mostly camelCasing scale names. a goal of this series of examples is to make it easier for someone learning to use d3 to understand what is happening. One way to do that is to make a whole new example at each new conceptual change.
do check out the other examples in this world map series:
world map 00 original example
world map 01 fix tooltip value
world map 02 d3 v4
world map 03 es2015 + update code style
world map 04 manual breaks + threshold scale
world map 05 linear breaks + quantize scale
world map 06 linear breaks + quantiles scale
world map 07 Jenks natural breaks
world map 08 ckmeans cluster max breaks
world map 09 ckmeans cluster min breaks