check-exercises.hs redundant import warning after GHC 7.10.x

[petertseng]

Travis keeps warning with:

_test/check-exercises.hs:18:1: warning: [-Wunused-imports]
    The import of ‘Control.Applicative’ is redundant
      except perhaps to import instances from ‘Control.Applicative’
    To import instances alone, use: import Control.Applicative()

Should check whether that's required. If not required, remove the line completely. If required, add the ().

[rbasso]

This warning is cause by Prelude exporting some functions from Control.Applicative after GHC version 7.10.x.

If we remove this line,check-exercises.hs it will not compile in older versions:

    Not in scope: `<$>'
    Perhaps you meant `</>' (imported from System.FilePath)

Functor-Applicative-Monad Proposal
GHC 7.10.x Migration Guide

The last link has some solutions to avoid this warning.