Update China Mirror URL to the New Version (#708)

npm.taobao.org is now redirect to npmmirror.com, use the new URL instead.

README.md

@@ -223,7 +223,7 @@ Display diagnostics to help resolve problems:
 If you would like to use a different Node.js mirror which has the same layout as the default <https://nodejs.org/dist/>, you can define `N_NODE_MIRROR`.
 The most common example is from users in China who can define:
 
-    export N_NODE_MIRROR=https://npm.taobao.org/mirrors/node
+    export N_NODE_MIRROR=https://npmmirror.com/mirrors/node
 
 If the custom mirror requires authentication you can add the [url-encoded](https://urlencode.org) username and password into the URL. e.g.