fix(guides) Fix errors in caching.md (#3059)

* fix errors in caching.md

1. use `new CleanWebpackPlugin()` instead of `new CleanWebpackPlugin(['dist'])`
2. use `hash` insteadif `contenthash `

* Update caching.md

Author: chenyinkai

src/content/guides/caching.md

@@ -106,7 +106,7 @@ __webpack.config.js__
     entry: './src/index.js',
     plugins: [
       // new CleanWebpackPlugin(['dist/*']) for < v2 versions of CleanWebpackPlugin
-      new CleanWebpackPlugin(['dist']),
+      new CleanWebpackPlugin(),
       new HtmlWebpackPlugin({
         title: 'Caching'
       })
@@ -151,7 +151,7 @@ __webpack.config.js__
     entry: './src/index.js',
     plugins: [
       // new CleanWebpackPlugin(['dist/*']) for < v2 versions of CleanWebpackPlugin
-      new CleanWebpackPlugin(['dist']),
+      new CleanWebpackPlugin(),
       new HtmlWebpackPlugin({
         title: 'Caching'
       }),
@@ -266,7 +266,7 @@ __webpack.config.js__
     entry: './src/index.js',
     plugins: [
       // new CleanWebpackPlugin(['dist/*']) for < v2 versions of CleanWebpackPlugin
-      new CleanWebpackPlugin(['dist']),
+      new CleanWebpackPlugin(),
       new HtmlWebpackPlugin({
         title: 'Caching'
       }),