Vladimír Čunát b336ed89e6 zopfli: disable parallel building ...

It was failing often, e.g.:
https://hydra.nixos.org/build/32101335/nixlog/1/raw

2016-03-23 20:20:36 +01:00

..

default.nix

zopfli: disable parallel building

2016-03-23 20:20:36 +01:00