[feature request] Add Travis CI Configuration Generation in nirvana init.

[gaocegege]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

It will be awesome if we could generate the .travis.yml together with the code base and Makefile.

[kdada]

It's a good idea for simplifying users' open-source projects. But it's not suitable for everyone. So I think we can add a flag to nirvana init to generate config for Travis CI (or Circle CI).

[gaocegege]

SGTM. It is an addtional feature and not everyone needs this.