chore: correct the comments in KeepAlive.ts [skip ci]

- The timing of caching subtree was changed in vuejs#1984
- The attr fallthrough / scopedId issue is actually vuejs#1511 instead of vuejs#1513

packages/runtime-core/src/components/KeepAlive.ts

@@ -305,11 +305,11 @@ const KeepAliveImpl: ComponentOptions = {
  rawVNode.ssContent = vnode
  }
  }
- // #1513 it's possible for the returned vnode to be cloned due to attr
+ // #1511 it's possible for the returned vnode to be cloned due to attr
  // fallthrough or scopeId, so the vnode here may not be the final vnode
  // that is mounted. Instead of caching it directly, we store the pending
  // key and cache `instance.subTree` (the normalized vnode) in
- // beforeMount/beforeUpdate hooks.
+ // mounted/updated hooks.
  pendingCacheKey = key
 
  if (cachedVNode) {