fix: month-overlay-value slot not working in month-picker (fixes #821)

Author: Jasenkoo

src/VueDatePicker/components/MonthPicker/MonthPicker.vue

@@ -45,6 +45,9 @@
                         </template>
                     </YearModePicker>
                 </template>
+                <template v-if="$slots[`month-overlay-value`]" #item="{ item }">
+                    <slot :name="`month-overlay-value`" :text="item.text" :value="item.value" />
+                </template>
             </SelectionOverlay>
         </template>
     </InstanceWrap>