Update README.md

Author: huoyuxin

README.md

@@ -1,5 +1,7 @@
 # HardSourceWebpackPlugin
 
+fix: cannot freeze caused by 'Cannot read property 'hash' of undefined'
+
 [![Build Status](https://travis-ci.org/mzgoddard/hard-source-webpack-plugin.svg?branch=master)](https://travis-ci.org/mzgoddard/hard-source-webpack-plugin) [![Build status](https://ci.appveyor.com/api/projects/status/761saaelxem01xo5/branch/master?svg=true)](https://ci.appveyor.com/project/mzgoddard/hard-source-webpack-plugin/branch/master)
 
 `HardSourceWebpackPlugin` is a plugin for webpack to provide an intermediate caching step for modules. In order to see results, you'll need to run webpack twice with this plugin: the first build will take the normal amount of time. The second build will be signficantly faster.