以下のURLからの引用です。
issue_closing_pattern: '([Cc]los(e([sd])?|ing)|[Ff]ix((e[sd])?|ing)) +((issue(s)? )?#\d+((,)? (and )?)?)+'
You can do somthing like :
fixes #8, #24, and #42
closing #26, #42 and #99
Fixing #42 and #24, #28
fixing issue #43 and issues #42
closed issues #83, #86 and #42
masterにマージしてプッシュした時にクローズされる模様。