cron: use terminal-notifier instead of dialog tool
cron: use terminal-notifier instead of dialog tool

`terminal-notifier` is installed via Homebrew, but `dialog` is manually
installed, so prefer the former.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent