fixes the issue of overly-tiny milestone columns

So I was having this issue, since our project has a lot of milestones in it:

![screenshot from 2014-03-24 11 22 14](https://f.cloud.github.com/assets/452041/2501280/aa978922-b36a-11e3-8c6b-3e07fdc90e27.png)

This pull request fixes it while preserving huboard's dynamic nature.