c358f519

Author: Greg Pfeil <greg@technomadic.org>

Committer: GitHub <noreply@github.com>

Get Signal from `nixpkgs-unstable`, not `master` (#244)

We’ll see if this is good enough – master carries a risk of rebuilding
Electron. If this doesn’t work, we can try Signal from `master`, but
pinning its Electron to `nixpkgs-unstable`. That guarantees we’ll build
Signal, but at least never Electron.