move LANGUAGE options to default-extensions

par.cabal

@@ -33,3 +33,5 @@ executable par
                      , text
   hs-source-dirs:      src
   default-language:    Haskell2010
+  default-extensions:  OverloadedStrings
+                     , ScopedTypeVariables

src/Main.hs

@@ -1,6 +1,3 @@
-{-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-
 module Main
   ( main
   ) where