Update Readme.md

Readme.md

@@ -55,7 +55,7 @@ By default `walint` prints lints in a hopefully human-readable manner. If the
 `--json` option is given, it will instead give a json that should conform to
 the following schema:
 
-```purescript
+```haskell
 -- | The main type of walint's output
 type Output = 
   { mapLints :: Map FilePath MapLint