docs(plugins): update DefinePlugin example to comply with recommendation (#2636)

Author: smonusbonus

src/content/plugins/define-plugin.md

@@ -5,6 +5,7 @@ contributors:
   - rouzbeh84
   - byzyk
   - EugeneHlushko
+  - smonusbonus
 ---
 
 The `DefinePlugin` allows you to create global constants which can be configured at **compile** time. This can be useful for allowing different behavior between development builds and release builds. If you perform logging in your development build but not in the release build you might use a global constant to determine whether logging takes place. That's where `DefinePlugin` shines, set it and forget it rules for development and release builds.
@@ -34,9 +35,7 @@ new webpack.DefinePlugin({
   BROWSER_SUPPORTS_HTML5: true,
   TWO: '1+1',
   'typeof window': JSON.stringify('object'),
-  'process.env': {
-    NODE_ENV: JSON.stringify(process.env.NODE_ENV)
-  }
+  'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV)
 });
 ```