chore: fix some broken links to v2 docs (#12839)

Author: Jinjiang

Diff for: examples/classic/elastic-header/index.html

@@ -32,7 +32,7 @@
       <draggable-header-view>
         <template slot="header">
           <h1>Elastic Draggable SVG Header</h1>
-          <p>with <a href="https://vuejs.org">Vue.js</a> + <a href="http://dynamicsjs.com">dynamics.js</a></p>
+          <p>with <a href="https://v2.vuejs.org">Vue.js</a> + <a href="http://dynamicsjs.com">dynamics.js</a></p>
         </template>
         <template slot="content">
           <p>Note this is just an effect demo - there are of course many additional details if you want to use this in production, e.g. handling responsive sizes, reload threshold and content scrolling. Those are out of scope for this quick little hack. However, the idea is that you can hide them as internal details of a Vue.js component and expose a simple Web-Component-like interface.</p>

Diff for: examples/classic/todomvc/app.js

@@ -55,7 +55,7 @@ var app = new Vue({
   },
 
   // computed properties
-  // https://vuejs.org/guide/computed.html
+  // https://v2.vuejs.org/v2/guide/computed.html
   computed: {
     filteredTodos: function () {
       return filters[this.visibility](this.todos)
@@ -129,7 +129,7 @@ var app = new Vue({
 
   // a custom directive to wait for the DOM to be updated
   // before focusing on the input field.
-  // https://vuejs.org/guide/custom-directive.html
+  // https://v2.vuejs.org/v2/guide/custom-directive.html
   directives: {
     'todo-focus': function (el, binding) {
       if (binding.value) {

Diff for: examples/classic/todomvc/readme.md

@@ -3,16 +3,16 @@
 > Vue.js is a library for building interactive web interfaces. 
 It provides data-driven, nestable view components with a simple and flexible API.
 
-> _[Vue.js - vuejs.org](https://vuejs.org)_
+> _[Vue.js - v2.vuejs.org](https://v2.vuejs.org)_
 
 ## Learning Vue.js
-The [Vue.js website](https://vuejs.org/) is a great resource to get started.
+The [Vue.js website](https://v2.vuejs.org/) is a great resource to get started.
 
 Here are some links you may find helpful:
 
-* [Official Guide](https://vuejs.org/guide/)
-* [API Reference](https://vuejs.org/api/)
-* [Examples](https://vuejs.org/examples/)
+* [Official Guide](https://v2.vuejs.org/guide/)
+* [API Reference](https://v2.vuejs.org/api/)
+* [Examples](https://v2.vuejs.org/examples/)
 
 Get help from other Vue.js users:
 

Diff for: src/compiler/codegen/index.ts

@@ -259,7 +259,7 @@ export function genFor(
     state.warn(
       `<${el.tag} v-for="${alias} in ${exp}">: component lists rendered with ` +
         `v-for should have explicit keys. ` +
-        `See https://vuejs.org/guide/list.html#key for more info.`,
+        `See https://v2.vuejs.org/v2/guide/list.html#key for more info.`,
       el.rawAttrsMap['v-for'],
       true /* tip */
     )