(fix) add indexId to avoid animation on _id change

Author: antoine92190

src/lib/Room/Room.vue

@@ -66,7 +66,7 @@
 						</infinite-loading>
 					</transition>
 					<transition-group :key="roomId" name="vac-fade-message" tag="span">
-						<div v-for="(m, i) in messages" :key="m._id">
+						<div v-for="(m, i) in messages" :key="m.indexId || m._id">
 							<message
 								:current-user-id="currentUserId"
 								:message="m"