Can't use Nix with 16.04

Setting language: nix seems to override my dist: xenial setting. See

It seems to me that the failure is coming from your script’s failure to clone ghc from their GitLab installation.

I don’t know what happened, but the latest build gets past that spot.

The script’s failure is because it’s running on Ubuntu 14.04. The latest build succeeded because I installed Nix manually instead of using language: nix.