Don't mention Ruby compatibility in contribution instructions

It will be caught by CI anyways and it gets out of date easily.

CONTRIBUTING.md

@@ -115,35 +115,32 @@ Here's a quick guide:
    bundle exec rspec spec/ransack/search_spec.rb -e "accepts a context option"
    ```
 
-5. Hack away! Please use Ruby features that are compatible down to Ruby 2.3.
-   Since version 2.3.1, Ransack no longer maintains Ruby 2.2 compatibility.
-
-6. Add tests for your changes. Only refactoring and documentation changes
+5. Add tests for your changes. Only refactoring and documentation changes
    require no new tests. If you are adding functionality or fixing a bug, we
    need a test!
 
-7. Make the tests pass.
+6. Make the tests pass.
 
-8. Update the Change Log. If you are adding new functionality, document it in
+7. Update the Change Log. If you are adding new functionality, document it in
    the README.
 
-9. Make sure git knows your name and email address in your `~/.gitconfig` file:
+8. Make sure git knows your name and email address in your `~/.gitconfig` file:
 
    ```sh
    git config --global user.name "Your Name"
    git config --global user.email "contributor@example.com"
    ```
 
-10. Commit your changes (`git commit -am 'Add feature/fix bug/improve docs'`).
+9. Commit your changes (`git commit -am 'Add feature/fix bug/improve docs'`).
     If your pull request only contains documentation changes, please remember
     to add `[skip ci]` to the beginning of your commit message so the CI
     test suite doesn't :runner: needlessly.
 
-11. If necessary, rebase your commits into logical chunks, without errors. To
+10. If necessary, rebase your commits into logical chunks, without errors. To
    interactively rebase and cherry-pick from, say, the last 10 commits:
    `git rebase -i HEAD~10`, then `git push -f`.
 
-12. Push the branch up to your fork on GitHub
+11. Push the branch up to your fork on GitHub
    (`git push origin my-new-feature`) and from GitHub submit a pull request to
    Ransack's `main` branch.