upgraded to specs2 2.2-SNAPSHOT

I changed the `contain(a, b, c).only` to `contain(exactly(a, b, c))` and simplified the setting of the `sequential` argument for mutable specifications.

I have also fixed the `havePair` calls to use a proper pair. Instead of writing `havePair("a", "b")` I wrote `havePair("a" -> "b")` and all the `-Xlint` warnings have been removed now.