completion: add human and auto: date format

human was introduced in acdd37769d
auto:* was introduced in 2fd7c22992

Those formats were missing when other values were added to completion
at 5a59a2301f

Signed-off-by: Yoichi Nakayama <yoichi.nakayama@gmail.com>
Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2001,7 +2001,7 @@ __git_log_shortlog_options="
 "
 
 __git_log_pretty_formats="oneline short medium full fuller reference email raw format: tformat: mboxrd"
-__git_log_date_formats="relative iso8601 iso8601-strict rfc2822 short local default raw unix format:"
+__git_log_date_formats="relative iso8601 iso8601-strict rfc2822 short local default human raw unix auto: format:"
 
 _git_log ()
 {