Fixes #812. Text Salience Maps Tutorial.

[iamshnoo]

• Fixed a typo in website/package.json
• Tutorial contents

[RyanMullins]

@jameswex @iftenney Note captions as left as TODOs intentionally as we're going to 1) convert some images to GIFs and need to capture the narrative of those GIFs, and 2) annotate the static images using the typical LIT callout styles and will need to write the captions with those annotations in mind.