Fix TypeError: object is not a function

Newer version of mathjs don't return a constructor function anymore, but a singleton.
Merge pull request #2 from despairblue/patch-1

Fix TypeError: object is not a function
Release version 0.3.0 and update package dependencies
Requires mathjs >= 0.25.0 (version where library returns a default instance)
https://github.com/josdejong/mathjs/blob/master/HISTORY.md#2014-07-01-version-0250
Moved to hubot-scripts
Merge remote-tracking branch 'upstream/master'