add Travis CI

.travis.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+#
+# Travis CI specific build script
+#
+set -euo pipefail
+
+./build
+
+if [[ "$TRAVIS_BRANCH" = master && -z "$TRAVIS_PULL_REQUEST_BRANCH" ]]; then
+  ./docker-login "$CI_REGISTRY" "$CI_REGISTRY_USER" "$CI_REGISTRY_PASSWORD"
+  ./push-all "$CI_REGISTRY_PREFIX" "$IMAGE_TAG"
+else
+  echo "=== not pushing on non-master ==="
+fi

.travis.yml

@@ -0,0 +1,13 @@
+language: nix
+
+nix: 2.2.1
+
+matrix:
+  include:
+  - name: nixos-unstable
+    env: NIX_PATH=nixpkgs=channel:nixos-unstable IMAGE_TAG=latest
+  - name: nixos-18.09
+    env: NIX_PATH=nixpkgs=channel:nixos-18.09 IMAGE_TAG=nixos-18.09
+
+script:
+  - nix-shell --run ./.travis.sh