nix-build on current master fails to evaluate.

git clone https://github.com/LumiGuide/haskell-opencv.git

nix-build

```error: Please be informed that this pseudo-package is not the only part of
       Nixpkgs that fails to evaluate. You should not evaluate entire Nixpkgs
       without some special measures to handle failing packages, like those taken
       by Hydra.

```

bit of show stopper... or is it just me?