docs(README): Fix ExtractTextPlugin example (#590)

charlesponti · joshwiens · commit b92c94194be1 · 2017-08-12T19:04:54.000-05:00
There was an extra `]` in the example
diff --git a/README.md b/README.md
@@ -488,7 +488,6 @@ module.exports = {
         })
       ]
     : []
-  ]
 }
 ```
 
