build: clean up versions

Also quote the version numbers, so Travis doesn't try to test fstream
against Node 0.1.

Author: othiym23

.travis.yml

@@ -1,9 +1,9 @@
 language: node_js
 node_js:
-  - iojs
-  - 0.12
-  - 0.10
-  - 0.8
+  - "6"
+  - "4"
+  - "0.10"
+  - "0.12"
 before_install:
   - "npm config set spin false"
   - "npm install -g npm/npm"