Improve wording for tagged people on tag page

That's actually a leftover and should be removed, it's a legacy from the time we used a translation platform that didn't provide these keys for languages that need them. WebTranslateIt does this, so that should actually be dropped in the people key. `I18n.t('i18n.plural.keys') #=> [:one, :other]`. `zero` is a special key used by all locales: https://github.com/svenfuchs/i18n/blob/master/lib/i18n/backend/pluralization.rb#L34