not support less node 6

Scrum · Scrum · commit 1578c0e3744c · 2016-06-03T15:37:09.000+03:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,5 @@
 language: node_js
 node_js:
   - v6
-  - v5
-  - v4
 after_success:
   - './node_modules/.bin/nyc report --reporter=text-lcov | ./node_modules/.bin/coveralls'
