git: Disable OS X keychain helper Closes Linuxbrew/linuxbrew#1
git: Disable OS X keychain helper Closes Linuxbrew/linuxbrew#1

rwhogg/homebrew-core,rwhogg/homebrew-core,maxim-belkin/homebrew-core,forevergenin/homebrew-core,LinuxbrewTestBot/homebrew-core,maxim-belkin/homebrew-core,Linuxbrew/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core,forevergenin/homebrew-core