Merge pull request #1454 from mistydemeo/travis_drop_node_4

chore(travis): drop Node 4, add Node 10

.travis.yml

@@ -1,8 +1,8 @@
 language: node_js
 node_js:
+  - "10"
   - "8"
   - "6"
-  - "4"
 notifications:
   email: false
 sudo: false