I would put master here yes.

The .travis.yml is setup to build all branches, but only one can be reported in the README (unfortunately, I imagine that will change at some point).

So you will want to merge this change, then create a travis account that is linked to 
cocos2d/cocos2d-x.  Once it is configured you can create a CL to change this image URL to point
to cocos2d/cococs2d-x rather than sbc100/cocos2d-x.