Fix typo in 'component' (#3978)

Author: AlexandreBonneau

src/core/vdom/vnode.js

@@ -12,7 +12,7 @@ export default class VNode {
   key: string | number | void;
   componentOptions: VNodeComponentOptions | void;
   child: Component | void; // component instance
-  parent: VNode | void; // compoennt placeholder node
+  parent: VNode | void; // component placeholder node
   raw: boolean; // contains raw HTML? (server only)
   isStatic: boolean; // hoisted static node
   isRootInsert: boolean; // necessary for enter transition check