Added hlint into CI

Author: katevi

.travis.yml

@@ -23,4 +23,4 @@ install:
 script:
 # Build the package, its tests, and its docs and run the tests
 - stack --no-terminal test --haddock --no-haddock-deps
-
+- curl -sSL https://raw.github.com/ndmitchell/hlint/master/misc/run.sh | sh -s .

package.yaml

@@ -33,6 +33,7 @@ dependencies:
 - megaparsec
 - parseargs
 - prettyprinter >= 1.7.0
+- hlint
 
 ghc-options: 
     -Wall