d3: __proto__ vs Object.create

d3.min.js Throws a warning in Firefox

> mutating the [[Prototype]] of an object will cause your code to run very slowly; instead create the object with the correct initial [[Prototype]] value using Object.create

https://github.com/mbostock/d3/issues/1805
http://stackoverflow.com/questions/15339550/difference-between-proto-link-and-object-create