401: Update version for the next release (v0.21.0) r=brunoocasali a=brunoocasali

This version makes this package compatible with Meilisearch v0.30.0 🎉
Check out the changelog of [Meilisearch v0.30.0](https://github.com/meilisearch/meilisearch/releases/tag/v0.30.0) for more information on the changes.

## 🚀 Enhancements

- Add `MeilisearchClient#cancel_tasks` (#392) `@brunoocasali` 
- Add `MeilisearchClient#swap_indexes` (#393) `@brunoocasali` 
- Add `MeilisearchClient#delete_tasks` (#394) `@brunoocasali` 
- Add support to finite pagination by using `page` and `hits_per_page` like `index.search('', { page: 1, hits_per_page: 10 })`
- Add filters for tasks resources (#391) `@brunoocasali` 
  - `uids` filter parameter for `MeilisearchClient#get_tasks({ uids: [1, 2, 3] })`
  - `canceled_by` filter parameter for `MeilisearchClient#get_tasks({ canceled_by: [99, 100]})`
  - `before_enqueued_at` and `after_enqueued_at` filter parameter for `MeilisearchClient#get_tasks({ before_enqueued_at: DateTime.new(2022), after_enqueued_at: '2022-01-20' })`
  - `before_finished_at` and `after_finished_at` filter parameter for `MeilisearchClient#get_tasks({ before_finished_at: DateTime.new(2022), after_finished_at: '2022-01-20' })`
  - `before_started_at` and `after_started_at` filter parameter for `MeilisearchClient#get_tasks({ before_started_at: DateTime.new(2022), after_started_at: '2022-01-20' })`

## ⚠️  Breaking Changes

- Update filters for tasks resources (#391) `@brunoocasali` 
  - `index_uid` query parameter is renamed `index_uids` when querying `MeilisearchClient#get_tasks`
  - `type` query parameter is renamed `types` when querying `MeilisearchClient#get_tasks`
  - `status` query parameter is renamed `statuses` when querying `MeilisearchClient#get_tasks`

## 💅 Misc

* Fix broken CI after rubocop upgrade (#381) `@jonatanrdsantos`
* Add new code-samples for matching_strategy (#384) `@thicolares`
* Improve indexes names in tests (#385) `@thicolares`

Thanks again to `@brunoocasali,` `@dibashthapa,` `@jonatanrdsantos,` and `@thicolares!` 🎉


Co-authored-by: Bruno Casali <brunoocasali@gmail.com>