RouteT: More stack-efficient (*>)

[rhendric]

To see the difference, run this file before and after patch with GHCRTS=-K1m cabal exec runghc:

import Web.Routes.RouteT

times :: Applicative f => Integer -> f a -> f a
times 1 m = m
times n m = m *> times (n - 1) m

main :: IO ()
main = unRouteT (times 100000 $ pure ()) $ \_ _ -> mempty