Node addon v6 job fails on osx

https://travis-ci.org/tugrul/cryptian/jobs/533851458

It looks like failed by missing new c++ feature on node v6 build job.

how can i specifiy c++11 flag for only v6 build job?

I found problem -stdlib=libc++ was missing v6 build environment.

I just add xcode_settings to binding.gyp file and problem is fixed.

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