config: consistently format $variables in monospaced font We don't consistently use `backticks` for formatting shell variables. This patch improves the consistency on shell variables (and a few nearby mentions of "gpg" commands), though it still doesn't straighten out the use of "quotes." Signed-off-by: Brian Norris <computersforpeace@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>