Update zsh-async to fix issue with zsh 5.3
Update zsh-async to fix issue with zsh 5.3

sindresorhus/pure,supercrabtree/pure,joshuarubin/dotfiles,joshuarubin/dotfiles,DFurnes/purer,dmiedema/pure,jaredru/zsh-pure,joshuarubin/dotfiles,forivall/pure,kgrz/pure,joshuarubin/dotfiles,mafredri/pure