fix: should pin major version in CDN links (#2717)

Otherwise, the link would point to a different major version after
Vue 3 moves to the `latest` dist-tag, which breaks examples; and some of
the links would be broken.

Author: haoqunjiang

src/v2/guide/comparison.md

@@ -111,7 +111,7 @@ React is renowned for its steep learning curve. Before you can really get starte
 While Vue scales up just as well as React, it also scales down just as well as jQuery. That's right - to get started, all you have to do is drop a single script tag into the page:
 
 ``` html
-<script src="https://cdn.jsdelivr.net/npm/vue"></script>
+<script src="https://cdn.jsdelivr.net/npm/vue@2"></script>
 ```
 
 Then you can start writing Vue code and even ship the minified version to production without feeling guilty or having to worry about performance problems.

src/v2/guide/index.md

@@ -24,14 +24,14 @@ The easiest way to try out Vue.js is using the [Hello World example](https://cod
 
 ``` html
 <!-- development version, includes helpful console warnings -->
-<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
+<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
 ```
 
 or:
 
 ``` html
 <!-- production version, optimized for size and speed -->
-<script src="https://cdn.jsdelivr.net/npm/vue"></script>
+<script src="https://cdn.jsdelivr.net/npm/vue@2"></script>
 ```
 
 The [Installation](installation.html) page provides more options of installing Vue. Note: We **do not** recommend that beginners start with `vue-cli`, especially if you are not yet familiar with Node.js-based build tools.

src/v2/guide/installation.md

@@ -41,7 +41,7 @@ Simply download and include with a script tag. `Vue` will be registered as a glo
 For prototyping or learning purposes, you can use the latest version with:
 
 ``` html
-<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
+<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
 ```
 
 For production, we recommend linking to a specific version number and build to avoid unexpected breakage from newer versions:
@@ -84,7 +84,7 @@ Vue provides an [official CLI](https://github.com/vuejs/vue-cli) for quickly sca
 
 ## Explanation of Different Builds
 
-In the [`dist/` directory of the NPM package](https://cdn.jsdelivr.net/npm/vue/dist/) you will find many different builds of Vue.js. Here's an overview of the difference between them:
+In the [`dist/` directory of the NPM package](https://cdn.jsdelivr.net/npm/vue@2/dist/) you will find many different builds of Vue.js. Here's an overview of the difference between them:
 
 | | UMD | CommonJS | ES Module (for bundlers) | ES Module (for browsers) |
 | --- | --- | --- | --- | --- |
@@ -101,7 +101,7 @@ In the [`dist/` directory of the NPM package](https://cdn.jsdelivr.net/npm/vue/d
 
 - **Runtime**: code that is responsible for creating Vue instances, rendering and patching virtual DOM, etc. Basically everything minus the compiler.
 
-- **[UMD](https://github.com/umdjs/umd)**: UMD builds can be used directly in the browser via a `<script>` tag. The default file from jsDelivr CDN at [https://cdn.jsdelivr.net/npm/vue](https://cdn.jsdelivr.net/npm/vue) is the Runtime + Compiler UMD build (`vue.js`).
+- **[UMD](https://github.com/umdjs/umd)**: UMD builds can be used directly in the browser via a `<script>` tag. The default file from jsDelivr CDN at [https://cdn.jsdelivr.net/npm/vue@2](https://cdn.jsdelivr.net/npm/vue@2) is the Runtime + Compiler UMD build (`vue.js`).
 
 - **[CommonJS](http://wiki.commonjs.org/wiki/Modules/1.1)**: CommonJS builds are intended for use with older bundlers like [browserify](http://browserify.org/) or [webpack 1](https://webpack.github.io). The default file for these bundlers (`pkg.main`) is the Runtime only CommonJS build (`vue.runtime.common.js`).
 

src/v2/guide/typescript.md

@@ -4,13 +4,13 @@ type: guide
 order: 403
 ---
 
-> [Vue CLI](https://cli.vuejs.org) provides built-in TypeScript tooling support. 
+> [Vue CLI](https://cli.vuejs.org) provides built-in TypeScript tooling support.
 
 ## Official Declaration in NPM Packages
 
 A static type system can help prevent many potential runtime errors, especially as applications grow. That's why Vue ships with [official type declarations](https://github.com/vuejs/vue/tree/dev/types) for [TypeScript](https://www.typescriptlang.org/) - not only in Vue core, but also for [vue-router](https://github.com/vuejs/vue-router/tree/dev/types) and [vuex](https://github.com/vuejs/vuex/tree/dev/types) as well.
 
-Since these are [published on NPM](https://cdn.jsdelivr.net/npm/vue/types/), and the latest TypeScript knows how to resolve type declarations in NPM packages, this means when installed via NPM, you don't need any additional tooling to use TypeScript with Vue.
+Since these are [published on NPM](https://cdn.jsdelivr.net/npm/vue@2/types/), and the latest TypeScript knows how to resolve type declarations in NPM packages, this means when installed via NPM, you don't need any additional tooling to use TypeScript with Vue.
 
 ## Recommended Configuration
 
@@ -195,7 +195,7 @@ If you find type inference or member completion isn't working, annotating certai
 ```ts
 import Vue, { PropType } from 'vue'
 
-interface ComplexMessage { 
+interface ComplexMessage {
   title: string,
   okMessage: string,
   cancelMessage: string
@@ -204,7 +204,7 @@ const Component = Vue.extend({
   props: {
     name: String,
     success: { type: String },
-    callback: { 
+    callback: {
       type: Function as PropType<() => void>
     },
     message: {