Update tmux.kak
Update tmux.kak

When $1 or ${kak_selection} start with dash, like "-1", the command will fail, because tmux think it's an argument flag.
-- prevent this.
Also the doc (append new line) is no longer valid.
lenormf/kakoune,Somasis/kakoune,Somasis/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,mawww/kakoune,lenormf/kakoune,casimir/kakoune,mawww/kakoune,Somasis/kakoune,mawww/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,casimir/kakoune,jkonecny12/kakoune,casimir/kakoune,mawww/kakoune,danr/kakoune,casimir/kakoune,danr/kakoune,danr/kakoune,jkonecny12/kakoune,lenormf/kakoune,Somasis/kakoune,lenormf/kakoune,danr/kakoune,jkonecny12/kakoune,alexherbo2/kakoune