Fix webpack config example

Author: nklayman

docs/guide/configuration.md

@@ -49,10 +49,12 @@ module.exports = {
       chainWebpackRendererProcess: config => {
         // Chain webpack config for electron renderer process only
         // The following example will set IS_ELECTRON to true in your app
-        rendererConfig.plugin('define').tap(args => {
+        config.plugin('define').tap(args => {
           args[0]['IS_ELECTRON'] = true
           return args
         })
+        // If you do not return the config property, your app may break!
+        return config
       },
       // Use this to change the entrypoint of your app's main process
       mainProcessFile: 'src/myBackgroundFile.js'