bson.cabal: allow quickcheck-2.7 and friends

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
bson.cabal: add missing tests files to tarball

On attemt to build minimal test suite cabal errors out:
Preprocessing test suite 'bson-tests' for bson-0.2.4...

tests/Tests.hs:5:18:
    Could not find module `Data.Bson.Tests'
    Use -v to see a list of the files searched for.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>