Update cli-plugin.md

Author: kamilmysliwiec

content/openapi/cli-plugin.md

@@ -215,7 +215,7 @@ Now, the serialized metadata file must be loaded by the `SwaggerModule#loadPlugi
 ```typescript
 import metadata from './metadata'; // <-- file auto-generated by the "PluginMetadataGenerator"
 
-SwaggerModule.loadPluginMetadata(metadata); // <-- here
+await SwaggerModule.loadPluginMetadata(metadata); // <-- here
 const document = SwaggerModule.createDocument(app, config);
 ```