Failure to compile with older versions of GHC

[ivanperez-keera]

Error message:

[ 8 of 23] Compiling Audio ( src/Audio.hs, dist/build/haskanoid/haskanoid-tmp/Audio.o )
src/Audio.hs:40:32: Not in scope: `<$>'
src/Audio.hs:58:32: Not in scope: `<$>'

Complete log: https://travis-ci.org/ivanperez-keera/haskanoid/jobs/291139506

Explanation: (<$>) was only available in Control.Applicative in older versions of the base library. Modules that use (<$>) should import Control.Applicative (<$>).

[ivanperez-keera]

To fix it, make sure that every module that uses (<$>) imports Control.Applicative (<$>).

A successful PR should compile fine on Travis CI.