fix typo

README.md

@@ -784,7 +784,7 @@ module.exports = {
 
 ## Demo14: Exposing global variables ([source](https://github.com/ruanyf/webpack-demos/tree/master/demo14))
 
-If you want to use some global variables, and don't want to includes them in the Webpack bundle, you can enable `externals` field in `webpack.config.js` ([official document](http://webpack.github.io/docs/library-and-externals.html)).
+If you want to use some global variables, and don't want to include them in the Webpack bundle, you can enable `externals` field in `webpack.config.js` ([official document](http://webpack.github.io/docs/library-and-externals.html)).
 
 For example, we have a `data.js`.