Setup Travis CI to run build in release mode

.travis.yml

@@ -0,0 +1,4 @@
+language: node_js
+node_js:
+    - lts/*
+cache: yarn

package.json

@@ -8,7 +8,7 @@
         "transifex-push": "gulp i18next && tx push --source",
         "transifex-pull": "tx pull --all --minimum-perc 1 --force && (git add locales/*.json && git commit locales/*.json -m 'Update translations' || true)",
         "layers": "node layers/josm/extract.js && node layers/collection/extract.js",
-        "test": "echo \"Error: no test specified\" && exit 1",
+        "test": "gulp",
         "prettier": "prettier --write '**/*'"
     },
     "husky": {