Change formatter prop from :format to :formatter

In vue2-datepicker 3.6.3 the `format` got renamed to `formatter`

See nextcloud-libraries/nextcloud-vue#1495 (comment)

Closes #2551

Signed-off-by: Michał Zając <michal.zajac@gmail.com>

src/components/Properties/PropertyDateTime.vue

@@ -60,7 +60,7 @@
 				:first-day-of-week="firstDay"
 				:type="inputType"
 				:readonly="isReadOnly"
-				:format="dateFormat"
+				:formatter="dateFormat"
 				class="property__value"
 				confirm
 				@confirm="debounceUpdateValue" />