bump scalatest to 2.2.2

mostly to pick up wildcard test-suite handling, e.g.:

    $ mvn test -Dsuites="*MdTag*"

(hammerlab has a helper around this for even more convenience; see
https://github.com/hammerlab/internal-tools/blob/master/scripts/mvn-utils/mvn-test)
Merge pull request #382 from ryan-williams/scalatest

bump scalatest to 2.2.2