Fix bug in example Chord diagram
Fix bug in example Chord diagram

This chart was not built to be re-drawn, so a slight modification is
necessary to enable multiple calls to `Chart#draw`.

tbranyen/d3.chart,misoproject/d3.chart,tbranyen/d3.chart,jugglinmike/d3.chart,jugglinmike/d3-experiments,misoproject/d3.chart