haskell.packages.ghcjs.ghcjs-base: fix build

The latest aeson doesn't build in ghcjs because it includes text-short
in its dependency tree, which hangs on checkPhase because it uses C FFI.
But since ghcjs-base has an upper bound on aeson<1.6 anyway, just
override it.

pkgs/development/haskell-modules/configuration-ghcjs.nix

@@ -20,6 +20,7 @@ self: super:
 
   ghcjs-base = dontCheck (self.callPackage ../compilers/ghcjs/ghcjs-base.nix {
     fetchFromGitHub = pkgs.buildPackages.fetchFromGitHub;
+    aeson = self.aeson_1_5_6_0;
   });
 
   # GHCJS does not ship with the same core packages as GHC.