Update ScalaTest.

Hi Sandro,

I'm starting to play around with Odds and so far I like it a lot. Especially for being the simplest and most functional probabilistic programming framework I've encountered so far.
I usually get comfortable with a project by playing around a little and doing minor changes that I like to contribute back as Pull Requests.
Is that OK with you?

Here I've updated Scalatest to the 2.0 release version which required minor changes, all tests still green :)

Best
  Martin