chore: upgrade node versions in ci.

Author: albin3

.travis.yml

@@ -9,7 +9,8 @@ node_js:
   - "v4.2.1"
   - "v4.3.0"
   - "v6.9.1"
-  - "v8.9.1"
+  - "v8.11.3"
+  - "v10.7.0"
 scripts: {
   "test": "make test"
   }