.travis.yml updates

* blank line
* Add Node.js versions:
  - 10.x (explicit)
  - 8.x
  - 6.14.x
  - 4.9.x (4.9.1)

Author: Christopher J. Brody

.travis.yml

@@ -1,9 +1,14 @@
 language: node_js
+
 node_js:
   - "stable"
+  - "10"
+  - "8"
+  - "6.14"
   - "6.5"
   - "6.4"
   - "6.3"
   - "5.12"
+  - "4.9"
   - "4.4"
   - "0.12"