2.0.0-alpha.4

Pre-release for Transformers.js v2.0.0

Same as https://github.com/xenova/transformers.js/releases/tag/2.0.0-alpha.3 with various improvements, including:

• GH actions to build demo site (https://xenova.github.io/transformers.js/)
• Calculate whisper mel filters when not present in processor's config.json