support ghc-7.8
fix deprecated warning

Module ‘Control.Monad.Instances’ is deprecated:
  This module now contains no instances and will be removed in
  the future
fix ghc 7.8's AMP warnings.

see also
 http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal#Missing_superclasses
for more information.