Build failure with mtl-2.3#4

``` Building library for rev-state-0.1.2.. [1 of 3] Compiling Control.Monad.Trans.RevState ( src/Control/Monad/Trans/RevState.hs, dist/build/Control/Monad/Trans/RevState.o, dist/build/Control/Monad/Trans/RevState.dyn_o ) src/Control/Monad/Trans/RevState.hs:59:10: error: Not in scope: type constructor or class ‘MonadFix’ Perhaps you meant ‘MonadFail’ (imported from Control.Monad) | 59 | instance MonadFix m => Monad (StateT s m) where | ^^^^^^^^ src/Control/Monad/Trans/RevState.hs:67:10: error: Not in scope: type constructor or class ‘MonadFix’ Perhaps you meant ‘MonadFail’ (imported from Control.Monad) | 67 | instance MonadFix m => Applicative (StateT s m) where | ^^^^^^^^ src/Control/Monad/Trans/RevState.hs:77:10: error: Not in scope: type constructor or class ‘MonadFix’ Perhaps you meant ‘MonadFail’ (imported from Control.Monad) | 77 | instance MonadFix m => MonadFix (StateT s m) where | ^^^^^^^^ src/Control/Monad/Trans/RevState.hs:77:24: error: Not in scope: type constructor or class ‘MonadFix’ Perhaps you meant ‘MonadFail’ (imported from Control.Monad) | 77 | instance MonadFix m => MonadFix (StateT s m) where | ^^^^^^^^ ```