Unwanted attributes appearing in index

## I want to report a bug:

### What is the current behavior?

I've defined an algolia_hooks.rb in the _plugins directory and filled it with classes/attrributes that I don't want indexed. However, the dashboard tells me that they still have been.

### What is your expected behavior?

None of these classes should turn up on the site's index.

### Git repository to reproduce the issue:

https://github.com/gazconroy/digital-comma/tree/gh-pages

### Ruby version used:

2.5

### Jekyll version used:

3.9

Reproduce the issue with the linked digital-comma repository, using Ruby 2.5 and Jekyll 3.9. Start by reading _plugins/algolia_hooks.rb and checking how the unwanted classes and attributes are configured for indexing. Done means those items no longer appear in the Algolia dashboard index.

Written by the indexing model from the issue text.