Test with Ruby 3.2 and 3.3 (#31)

* Add instructions about running the test suite

When making a contribution, it's useful to know how to run the test suite. Usually I would expect `rake` or `rake test` to work, but this project has no Rakefile, so I think it's fine to simply document how to run the test suite: `rspec spec`

* For development, use a more modern ruby version

* Test with Ruby 3.2 and 3.3

I believe this _should just work_ but I guess GitHub Actions CI will have the last word : )

* Exclude Ruby 2.5 and below (macos-latest won't support it)

.github/workflows/main.yml

@@ -11,7 +11,11 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        ruby-version: [3.1, 3.0, 2.7, 2.6, 2.5, 2.4, 2.3]
+        ruby-version: [3.3, 3.2, 3.1, 3.0, 2.7, 2.6, 2.5, 2.4, 2.3]
+        exclude:
+          - { os: macos-latest, ruby: '2.3' }
+          - { os: macos-latest, ruby: '2.4' }
+          - { os: macos-latest, ruby: '2.5' }
     runs-on: ${{ matrix.os }}
 
     steps:

.ruby-version

@@ -1 +1 @@
-2.7.3
+3.2.3

README.md

@@ -248,7 +248,13 @@ Keep in mind that the location of the Gemfile.lock/gems.locked file will be infe
 Contributing
 ------------
 
-Contributions are very welcome. Fork, fix, submit pulls.
+Contributions are very welcome. Fork, fix, submit pull requests.
+
+Before you submit your pull request, make sure that the test suite passes:
+
+```
+bundle exec rspec spec
+```
 
 Contribution is expected to conform to the [Contributor Covenant](https://github.com/jmmastey/bundler-stats/blob/master/CODE_OF_CONDUCT.md).