Revert "Temporarily disable OS X builds on Travis CI"
Revert "Temporarily disable OS X builds on Travis CI"

This reverts commit fef3871be2f6ed50335c57b9b495f07e44cacc9b.

jsoref/PowerShell,bmanikm/PowerShell,kmosher/PowerShell,bmanikm/PowerShell,PaulHigin/PowerShell,KarolKaczmarek/PowerShell,daxian-dbw/PowerShell,PaulHigin/PowerShell,bingbing8/PowerShell,daxian-dbw/PowerShell,daxian-dbw/PowerShell,bmanikm/PowerShell,KarolKaczmarek/PowerShell,jsoref/PowerShell,TravisEz13/PowerShell,jsoref/PowerShell,bingbing8/PowerShell,KarolKaczmarek/PowerShell,bmanikm/PowerShell,kmosher/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,jsoref/PowerShell,JamesWTruher/PowerShell-1,kmosher/PowerShell,JamesWTruher/PowerShell-1,jsoref/PowerShell,bingbing8/PowerShell,TravisEz13/PowerShell,TravisEz13/PowerShell,bingbing8/PowerShell,daxian-dbw/PowerShell,kmosher/PowerShell,JamesWTruher/PowerShell-1,PaulHigin/PowerShell,TravisEz13/PowerShell,KarolKaczmarek/PowerShell,KarolKaczmarek/PowerShell,bingbing8/PowerShell,PaulHigin/PowerShell,bmanikm/PowerShell