haskell-boxes: apply patch to fix build with GHC 8.4.1

pkgs/development/haskell-modules/configuration-ghc-8.4.x.nix

···
   # https://github.com/pikajude/stylish-cabal/issues/6
   stylish-cabal = dontHaddock super.stylish-cabal;
 
+  # https://github.com/treeowl/boxes/issues/29
+  boxes = appendPatch super.boxes (pkgs.fetchpatch
+    { url = https://github.com/asr/boxes/commit/f03e16cb8677a9d85687c641fe27a87e6fd94d54.patch;
+      sha256 = "179vkn6jimiy64dwyam04x8v981l3pfrq3ig97600vnkns3v8i6a";
+    });
+
 }