Get rickshaw working with recent Meteor

The extant meteor-rickshaw package on atmosphere isn't working with recent versions of Meteor for the following reasons:

1. `Rickshaw` is not exported by the package.js using `api.export()`
2. The code snippet that sets `d3` to `require("d3")` or `window.d3` doesn't work - it ends up setting `d3` to `undefined`. Since we have already imported the d3 variable we don't need this snippet at all.
3. Sundry reasons to update to the latest version of rickshaw (these may be more to do with my code than the package).

This pull request addresses all three and works for me. You may wish to verify/fix it your own way.