Add Node.js 4.0 to Travis CI target
Add Node.js 4.0 to Travis CI target

There is high prossibility that we'll move on to the next version. It
may be better to test for both 0.12 and 4.

sgkim126/beyond.ts,sgkim126/beyond.ts,noraesae/beyond.ts,noraesae/beyond.ts,SollmoStudio/beyond.ts,SollmoStudio/beyond.ts