Fix datetime mandatory

Signed-off-by: Jonas Rittershofer <jotoeri@users.noreply.github.com>

src/components/Questions/QuestionDate.vue

@@ -42,6 +42,7 @@
 				:placeholder="datetimePickerPlaceholder"
 				:show-second="false"
 				:type="datetimePickerType"
+				:input-attr="inputAttr"
 				@change="onValueChange" />
 		</div>
 	</Question>
@@ -95,6 +96,16 @@ export default {
 			}
 			return 'LL'
 		},
+
+		/**
+		 * All non-exposed props onto datepicker input-element.
+		 * @returns {Object}
+		 */
+		inputAttr() {
+			return {
+				required: this.mandatory,
+			}
+		},
 	},
 
 	methods: {