Unable to install gem on Ruby < 3.0

[tasercake]

Using ruby 2.7.4, I'm unable to install github_changelog_generator due to a dependency issue.

Reproducing

With Ruby < 3.0, install the github_changelog_generator gem:

# Ruby 2.7.4
$ gem install github_changelog_generator
ERROR:  Error installing github_changelog_generator:
	There are no versions of io-event (~> 1.0.0) compatible with your Ruby & RubyGems. Maybe try installing an older version of the gem you're looking for?
	io-event requires Ruby version >= 3.0. The current ruby version is 2.7.4.191.

Workaround

Switching to Ruby 3.0, the gem installs fine:

# Ruby 3.0.0
$ gem install github_changelog_generator

Successfully installed github_changelog_generator-1.16.4

As does installing a lower version of async first on Ruby 2.7.4:

# Ruby 2.7.4
$ gem install async -v '~> 1.29'
$ gem install github_changelog_generator

Successfully installed github_changelog_generator-1.16.4

It looks like async bumped their io-event requirement recently, which breaks compatibility with Ruby 2.x: socketry/async@d16f7fa

Perhaps the async dependency should be pinned to version 1 to maintain compatibility with Ruby 2?

---

Desktop

• OS: macOS Catalina (10.15.7)
• Browser: Chrome 96.0.4664.110
• Ruby: 2.7.4.191 (installed using rvm)

[olleolleolle]

Workarounds you can do yourself include:

• constraining versions of async to be used, using a Gemfile and Bundler. See Bundler's documentation. E.g. https://bundler.io/v2.2/guides/using_bundler_in_applications.html