[ticket/11407] Fix <dfn> description of "notification" option.

PHPBB3-11407
Merge remote-tracking branch 'remotes/nickv/ticket/11407' into develop

# By Joas Schilling
# Via Joas Schilling
* remotes/nickv/ticket/11407:
  [ticket/11407] Fix <dfn> description of "notification" option.