add Travis-CI to the repo

[zimbatm]

todo:

• setup Travis-CI on the repo
• test that it works

[lukateras]

I don't think that would work because this test requires NixOS (for nixos-rebuild), and I don't think that Travis CI uses NixOS (they are likely to use something like Debian with Nix installed).

[lukateras]

Without this, test would never fail.

[zimbatm]

set -e takes care of this

[lukateras]

Great! Didn't know about set -e.

[zimbatm]

fixed the test script so that it works on any system that has nix installed

[Mic92]

In doubt, it is possible to create VMs on non-nixos systems: nix-build '<nixpkgs/nixos>' -A vm -k -I nixos-config=./vm.nix

[lukateras]

It works on Debian!

[lukateras]

I think shell scripts should be portable. Also, changing evaluation rules makes it harder to reason about. Let's leave it at #!/bin/sh, set -e, and find.

[lukateras]

Sorry for force-pushing on top of your work, for reference, it's in fc032be7355ef8d1226fa77f0ef3a0c153e36100. Again, I think it makes the script more complex and I don't see any point in making it less verbose.

[zimbatm]

@yegortimoshenko it's fine to disagree but please stop merging things into master while we are having a discussion. Anyways, follow-up in #44

[lukateras]

@zimbatm I've only reverted your pull request to a previous state that we've agreed upon. The point of this pull request seemingly was to make Travis CI work and it works, so I've merged it.