Automatically set /dev/tty as STDIN on execute action

https://github.com/junegunn/fzf/issues/1360#issuecomment-788178140

  # Redirect /dev/tty to suppress "Vim: Warning: Input is not from a terminal"
  ls | fzf --bind "enter:execute(vim {} < /dev/tty)"

  # With this change, we can omit "< /dev/tty" part
  ls | fzf --bind "enter:execute(vim {})"