Squashed 'vendor/assets/javascripts/d3/plugins/' changes from 6795b89..5c6e4f0

5c6e4f0 Fix #38 bug in hexbin plugin.
30d7432 Fix a bug in hexbin.mesh.
31b9046 Use internal trig methods.
2045e85 Add d3.geo.twoPointEquidistant.

git-subtree-dir: vendor/assets/javascripts/d3/plugins
git-subtree-split: 5c6e4f0decea2372da9cb7c8cb6c1559e50a0a29
Merge commit '9ee5b68ea04df48aeaeff4a597c97ce3f6433a50'

* commit '9ee5b68ea04df48aeaeff4a597c97ce3f6433a50':
  Squashed 'vendor/assets/javascripts/d3/plugins/' changes from 6795b89..5c6e4f0
Bump gem version