Add gh command
Add gh command

This is to fix an issue in
https://github.com/olivierverdier/zsh-git-prompt/pull/30#issuecomment-26727414

wkentaro/zsh-git-prompt,TheAtomicGoose/zsh-git-prompt,waltflanagan/zsh-git-prompt,aclissold/zsh-git-prompt,tasyrkin/zsh-git-prompt,TiddoLangerak/zsh-git-prompt,megalithic/zsh-git-prompt,sk1418/zsh-git-prompt,sk1418/zsh-git-prompt,wkentaro/zsh-git-prompt,atanasenko/zsh-git-prompt,ToonSpin/zsh-git-prompt,aclissold/zsh-git-prompt,aclissold/zsh-git-prompt,mttrs/zsh-git-prompt,maebeale/.zsh-git-prompt,ToonSpin/zsh-git-prompt,tasyrkin/zsh-git-prompt,biggerfisch/zsh-git-prompt,megalithic/zsh-git-prompt,stepanv/zsh-git-prompt,TiddoLangerak/zsh-git-prompt,olivierverdier/zsh-git-prompt,waltflanagan/zsh-git-prompt,mttrs/zsh-git-prompt,biggerfisch/zsh-git-prompt,olivierverdier/zsh-git-prompt,atanasenko/zsh-git-prompt,stepanv/zsh-git-prompt,cevaris/zsh-git-prompt,cevaris/zsh-git-prompt,maebeale/.zsh-git-prompt,TheAtomicGoose/zsh-git-prompt