Rename generate_feed into generate_feeds as per Zola 0.19 breaking changes

[Horgix]

Current behavior

When building a site with Zola and this theme, or even just running zola check, it currently fails with the following:

Checking site...
Error: Failed to check the site
Error: TOML parse error at line 11, column 1
   |
11 | generate_feed = true
   | ^^^^^^^^^^^^^
unknown field `generate_feed`, expected one of `base_url`, `theme`, `title`, `description`, `default_language`, `languages`, `translations`, `generate_feeds`, `feed_limit`, `feed_filenames`, `hard_link_static`, `taxonomies`, `author`, `compile_sass`, `minify_html`, `build_search_index`, `ignored_content`, `ignored_static`, `mode`, `output_dir`, `preserve_dotfiles_in_output`, `link_checker`, `slugify`, `search`, `markdown`, `extra`

Explanation

As part of the Zola 0.19 release, the support for multiple feeds (Atom, RSS) was added (getzola/zola#2477). This resulted in the renaming of the generate_feed top level configuration key of Zola into generate_feeds (note the +s).

When coupled with the introduction of #[serde(deny_unknown_fields)] on the Zola configuration validation that was shipped at the same time, it not only means that the old name is no longer effective, but that it's now actually denied.

Also see getzola/zola#2566 for the upstream discussion.

Fix

This PR proposes to fix that by renaming all the occurrences of generate_feed into generate_feeds 🙂

Tested locally and it works fine.

[Speyll]

ty very much!