Fix for ghcjs 8.10

Author: hamishmack

test/js-template-haskell/default.nix

@@ -9,7 +9,8 @@ let
     src = testSrc "js-template-haskell";
     cabalProjectLocal = ''
       if arch(javascript)
-        extra-packages: ghci
+        if impl(ghc>9)
+          extra-packages: ghci
     '';
   };