[vim] Fix terminal buffer cleanup on Vim 8
[vim] Fix terminal buffer cleanup on Vim 8

Close #1172

janlazo/fzf,wilywampa/fzf,wilywampa/fzf,junegunn/fzf,janlazo/fzf,junegunn/fzf,stuha/wbr-zsh,janlazo/fzf,junegunn/fzf,infokiller/fzf,infokiller/fzf,infokiller/fzf,wilywampa/fzf