Update Rickshaw chart library

[Juha Mustonen]

There is reason to believe the Rickshaw library included in Atlasboard is out-of-date (no version info included) as it's API does not match with the official documentation:

• https://bitbucket.org/atlassian/atlasboard/src/HEAD/assets/third-party/rickshaw/?at=master
• https://github.com/shutterstock/rickshaw

Thus, update the library before more charts will get implemented on top of old API.

[Iván Loire]

Thanks, I bumped ricksaw to 1.5 with dbd5559 We will track versioning better from now on.