i18n: Plural form in vue file needed

[rakekniven]

server/apps/files/src/components/FilesListVirtual.vue

Line 24 in 15035dc

<span class="files-list__selected">{{ t('files', '{count} selected', { count: selectedNodes.length }) }}</span>

Reported at Transifex:
This string needs pluralization feature, because in some languages translation of "selected" differs between singular and plural.