Fix homebrew directory in aws plugin.
Fix homebrew directory in aws plugin.

Sometimes the output of ``homebrew --prefix`` and ``homebrew --prefix
awscli`` don't match, and the second is the correct call.

nunogt/oh-my-zsh,FrankSansC/oh-my-zsh,lightmanhk/oh-my-zsh,FrankSansC/oh-my-zsh,FrankSansC/oh-my-zsh,tekniklr/oh-my-zsh,FrankSansC/oh-my-zsh,lightmanhk/oh-my-zsh,nunogt/oh-my-zsh,tekniklr/oh-my-zsh,lightmanhk/oh-my-zsh,lightmanhk/oh-my-zsh