ci(travis): add build test to ci

Author: gr2m

.travis.yml

@@ -20,6 +20,9 @@ jobs:
       script: npm test
     - node_js: 10
       script: npm test
+    - node_js: lts/*
+      env: build test
+      script: npm run build
 
     # release stage: run semantic release & update the docs
     - stage: release