Upgrade D3 to 3.4.13

UThis is the latest upstream version, available at this URL:

  https://github.com/mbostock/d3/releases/tag/v3.4.13
Switch to a non-minified version of D3 to ease debugging

The addon will be gzipped anyways, so the size difference should
not matter too much (71k v. 51k).
Merge pull request #619 from fmarier/d3-update

D3 update