docs: update configuration example to import plugin from the main entry

Author: haoqunjiang

docs/guide/README.md

@@ -26,7 +26,7 @@ Vue Loader's configuration is a bit different from other loaders. In addition to
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   module: {

docs/migrating.md

@@ -17,7 +17,7 @@ Vue Loader v15 now requires an accompanying webpack plugin to function properly:
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   // ...

docs/ru/guide/README.md

@@ -26,7 +26,7 @@ npm install -D vue-loader vue-template-compiler
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   module: {
@@ -51,7 +51,7 @@ module.exports = {
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   mode: 'development',

docs/ru/migrating.md

@@ -17,7 +17,7 @@ Vue Loader v15 теперь для правильной работы требу
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   // ...

docs/zh/guide/README.md

@@ -26,7 +26,7 @@ Vue Loader 的配置和其它的 loader 不太一样。除了通过一条规则
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   module: {
@@ -51,7 +51,7 @@ module.exports = {
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   mode: 'development',

docs/zh/migrating.md

@@ -17,7 +17,7 @@ Vue Loader v15 现在需要配合一个 webpack 插件才能正确使用：
 
 ``` js
 // webpack.config.js
-const VueLoaderPlugin = require('vue-loader/lib/plugin')
+const { VueLoaderPlugin } = require('vue-loader')
 
 module.exports = {
   // ...