rvm安装时报gpg命令找不到的解决办法

Possible sources are:

• Package manager Homebrew:
  

  brew install gnupg gnupg2

or

$ brew install gpg2

or

$brew install gnupg

• Package manager MacPorts:

  sudo port install gnupg gnupg2

• Install from GPGTools, which also brings GUI applications and integration in Apple Mail

参考：http://stackoverflow.com/questions/27041885/how-to-resolve-gpg-command-not-found-error-during-rvm-installation