Add ++nested modifier to TabLeave autocommand

[benknoble]

This allows autocommands to fire for commands during s:goyo_off.

A prominent example would be any autocommands user's installed on the
ColorScheme event (e.g., to set User highlights, like I do in my Dotfiles)

This should provide a fix for #160. Of note, I only see issues in my statusline (which uses User highlights) when I hit e.g. gt from goyo—when I close the tab with :quit, everything works fine. So I've only added the nested modifier here.

[junegunn]

Hi, both Neovim and Vim version I have installed on my system don't understand ++nested, so please change it to nested for backward compatibility.

autocmd TabLeave    * nested call s:goyo_off()

(You can just fit in nested between * and call without extra spaces now.)

[benknoble]

@junegunn Done 👍