chore: fix typo (vuejs#7781)

Author: g-plane

src/core/vdom/vnode.js

@@ -26,7 +26,7 @@ export default class VNode {
   ssrContext: Object | void;
   fnContext: Component | void; // real context vm for functional nodes
   fnOptions: ?ComponentOptions; // for SSR caching
-  fnScopeId: ?string; // functioanl scope id support
+  fnScopeId: ?string; // functional scope id support
 
   constructor (
     tag?: string,