Fix two errors with the clientManifest (#19)

1. In the text, it said that `clientManifest` would only be used in `createBundleRenderer`. I tried it, and it works with the normal renderer, too.
2. The client build manifest is generated by the `vue-server-renderer/client-plugin`, not by `vue-server-renderer/server-plugin`

Author: danieldiekmeier

Diff for: en/api.md

@@ -82,9 +82,8 @@ See [Introducing the Server Bundle](./bundle-renderer.md) and [Build Configurati
 - #### `clientManifest`
 
   - 2.3.0+
-  - only used in `createBundleRenderer`
 
-  Provide a client build manifest object generated by `vue-server-renderer/server-plugin`. The client manifest provides the bundle renderer with the proper information for automatic asset injection into the HTML template. For more details, see [Generating clientManifest](./build-config.md#generating-clientmanifest).
+  Provide a client build manifest object generated by `vue-server-renderer/client-plugin`. The client manifest provides the bundle renderer with the proper information for automatic asset injection into the HTML template. For more details, see [Generating clientManifest](./build-config.md#generating-clientmanifest).
 
 - #### `inject`