Fix installation by pinning whois gem v4

[yoshikazusawa]

Pull Request Checklist

Is this in reference to an existing issue?

General

• [ ] Update Changelog following the conventions laid out here

• [ ] Update README with any necessary configuration snippets

• [ ] Binstubs are created if needed

• [ ] RuboCop passes

• [ ] Existing tests pass

New Plugins

• [ ] Tests

• [ ] Add the plugin to the README

• [ ] Does it have a complete header as outlined here

Purpose

The recent update of the whois gem to version 6.0.0 has raised the minimum required Ruby version to 3.0. https://rubygems.org/gems/whois/versions/6.0.0

This change has caused the sensu-install -p sensu-plugins-network-checks command to fail with the following error:

sensu-install -p sensu-plugins-network-checks
[SENSU-INSTALL] installing Sensu plugins ...
[SENSU-INSTALL] determining if Sensu gem 'sensu-plugins-network-checks' is already installed ...
false
[SENSU-INSTALL] Sensu plugin gems to be installed: ["sensu-plugins-network-checks"]
[SENSU-INSTALL] installing Sensu gem 'sensu-plugins-network-checks'
ERROR:  Error installing sensu-plugins-network-checks:
        whois requires Ruby version >= 3.0.

To address this issue, I have pinned the whois gem to the last compatible major version 4.

Known Compatibility Issues