Add new transition class name

- Modified transition class name needed for vue3.
- Add comment for vue version based classes.

Signed-off-by: Suren Neware <sneware9@in.ibm.com>
Change-Id: I3578ca7c45e71326e38888412a4f36c266b005a0
diff --git a/src/components/AppNavigation/AppNavigation.vue b/src/components/AppNavigation/AppNavigation.vue
index 233d496..fb50f5e 100644
--- a/src/components/AppNavigation/AppNavigation.vue
+++ b/src/components/AppNavigation/AppNavigation.vue
@@ -238,7 +238,8 @@
     transition: opacity $duration--fast-02 $exit-easing--productive;
   }
 
-  &.fade-enter,
+  &.fade-enter, // Remove this vue2 based only class when switching to vue3
+  &.fade-enter-from, // This is vue3 based only class modified from 'fade-enter'
   &.fade-leave-to {
     opacity: 0;
   }