upgrade .travis nodejs version

hakimel · hakimel · commit 3b4fabc8a780 · 2019-02-28T13:27:41.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 language: node_js
 node_js:
-  - 4
+  - 11
 after_script:
   - npm run build -- retire
