Drop v.12 from Travis (#496)

evenstensberg · hemanth · commit e5e4bf0a9b5d · 2016-12-30T19:46:48.000+05:30
`node v.12` is being left for EOL now and I don't see any reason to keep it supported in Travis. Merge is optional!
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,6 @@
 sudo: false
 language: node_js
 node_js:
-  - v0.12
   - v4
   - v5
   - v6
