fixed typo on line 15 (#4829)

Author: adamawang

src/core/vdom/helpers/normalize-children.js

@@ -12,7 +12,7 @@ import VNode, { createTextVNode } from 'core/vdom/vnode'
 
 // 1. When the children contains components - because a functional component
 // may return an Array instead of a single root. In this case, just a simple
-// nomralization is needed - if any child is an Array, we flatten the whole
+// normalization is needed - if any child is an Array, we flatten the whole
 // thing with Array.prototype.concat. It is guaranteed to be only 1-level deep
 // because functional components already normalize their own children.
 export function simpleNormalizeChildren (children: any) {