fix: undefined variables and wrong names

[GlintonLiao]

There are some mistakes in the template:

1. inside Experience.js, there is no rendererInstance attribute in the class, so it's passing undefined to the Render().
2. inside Loader.js, the class name is wrong.
3. There is no DracoLoader.releaseDecoderModule() method in this version, it became an instance method dispose() instead.

None of these mistakes will have an impact on the final result, but it's always good to fix them :)