Add Node 9 to Travis

Reorder the Node versions while we're at it to fail faster if something's wrong (because newer Node versions are faster than old)

Author: jwilsson

.travis.yml

@@ -4,11 +4,12 @@ sudo: false
 language: node_js
 
 node_js:
-  - "4"
-  - "5"
-  - "6"
-  - "7"
+  - "9"
   - "8"
+  - "7"
+  - "6"
+  - "5"
+  - "4"
 
 git:
   depth: 1