Add tranformers to benchmarks

[phadej]

Fixes:

..../attoparsec/Data/Attoparsec/Zepto.hs:41:8:
    Could not find module ‘Control.Monad.IO.Class’
    It is a member of the hidden package
‘transformers-0.4.2.0@trans_3eG64VdP2vzGjP6wJiCp5X’.
    Perhaps you need to add ‘transformers’ to the build-depends in your
.cabal file.
    Use -v to see a list of the files searched for.

[RyanGlScott]

Note that attoparsec's benchmarks are failing on recent Stackage builds due to this issue. (See commercialhaskell/stackage#1372 (comment))

[bgamari]

Thanks for bringing this to my attention, @RyanGlScott! I recently stepped up as a co-maintainer for attoparsec and intend to do a new release shortly (although at the moment things are quite busy with the imminent GHC release).

[bgamari]

@RyanGlScott I've pushed a new release to Hackage as 0.13.0.2. Thanks!