travis badge to be for master branch?

[tunnckoCore]

Because if some greenkeeper update fails it shows red badge on the readme and I think this isn't good. Users may think the master branch and published release fails, which isn't correct. It's not good for reputation of the package/repository, so I recently changed it in my readmes.

https://img.shields.io/travis/node-minibase/minibase.svg
https://img.shields.io/travis/node-minibase/minibase/master.svg

edit/updated