improvement(tmux/tmux.conf): update config to make tmux works in 3.0+ and below
improvement(tmux/tmux.conf): update config to make tmux works in 3.0+ and below

A breaking change happened when tmux 3.0 was released; see the
extraction from the CHANGES file:

* INCOMPATIBLE: tmux's configuration parsing has changed to use yacc(1).
  There is one incompatible change: a \ on its own must be escaped or
  quoted as either \\ or '\' (the latter works on older tmux versions).

See: https://raw.githubusercontent.com/tmux/tmux/3.0/CHANGES

shoichiaizawa/dotfiles,shoichiaizawa/dotfiles,shoichiaizawa/dotfiles