Set COMMIT_EDITMSG to 80-char limit in .dir-locals.el

.dir-locals.el

@@ -6,5 +6,6 @@
  (makefile-mode . ((indent-tabs-mode . t)))
  (asm-mode . ((indent-tabs-mode . t)))
  (shell-script-mode . ((indent-tabs-mode . t)))
+ ("\.git/COMMIT_EDITMSG" . ((nil . ((fill-column . 80)))))
  ((nil . ((truncate-lines . t)))
           (text-mode . ((eval . ((turn-on-auto-fill)))))))