fix: render custom template in day slot

Author: farnabaz

src/components/core/calendar.vue

@@ -44,7 +44,11 @@
 
           <slot
             v-bind="props"
-            name="day"/>
+            name="day">
+            <div class="vuec-default-day">
+              {{ props.date.format('D') }}
+            </div>
+          </slot>
 
         </template>
 

src/components/core/month.vue

@@ -35,7 +35,6 @@
           @blur="$emit('blur', $event)"
         >
           <template
-            v-if="$slots.day"
             slot="day"
             slot-scope="props">