.travis.yml: Xcode 7.3, one OS X build. (#3531)
.travis.yml: Xcode 7.3, one OS X build. (#3531)

We don't need three OS X build here (I mean really we don't need one) considering they are handled by Jenkins now.
andrewjpage/homebrew-science,kozo2/homebrew-science,pditommaso/homebrew-science,DabeDotCom/homebrew-science,dpo/homebrew-science,quantumsteve/homebrew-science,heuermh/homebrew-science,philippbayer/homebrew-science,joshbode/homebrew-science,parcollet/homebrew-science,maplesond/homebrew-science,aeantipov/homebrew-science