an es2015 d3v4 iteration on the block network fade from @jalapic
mouse over a node to see that node and it's first-degree neighbors highlighted (along with the links that connect them)
see also graph neighbors on mouseover from @micahstubbs
forked from micahstubbs's block: network fade | d3v4 es2015
Modified http://d3js.org/d3.v4.js to a secure url
https://d3js.org/d3.v4.js