traivis: Set language to Haskell98, install Cabal

We need a more up to date version of Cabal to avoid some bugs it seems,
so lets try that.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Fix build with QuickCheck < 2.6

Signed-off-by: Austin Seipp <aseipp@pobox.com>