`rubocop --version` crashes on fresh ruby environment

[Fletcher Porter]

After purging my ruby environment

```
sudo gem uninstall $(gem list --installed --no-versions)
sudo apt remove ruby* rubocop rake --yes
sudo apt autoremove --yes
sudo apt purge --yes
dpkg --list | grep ruby > /dev/null
if [ $? -eq 1 ]; then echo "no more ruby"; fi
```

And installing rubocop

```
sudo apt install rubocop ruby ruby-full
```

I get this error.

```
$ rubocop --version
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:10: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:29: warning: constant Gem::ConfigMap is deprecated
/usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:30: warning: constant Gem::ConfigMap is deprecated
Traceback (most recent call last):
 10: from /usr/bin/rubocop:6:in `<main>'
  9: from /usr/local/lib/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:85:in `require'
  8: from /usr/local/lib/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:85:in `require'
  7: from /usr/lib/ruby/vendor_ruby/rubocop.rb:14:in `<top (required)>'
  6: from /usr/local/lib/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:85:in `require'
  5: from /usr/local/lib/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:85:in `require'
  4: from /usr/lib/ruby/vendor_ruby/unicode/display_width.rb:2:in `<top (required)>'
  3: from /usr/lib/ruby/vendor_ruby/unicode/display_width.rb:2:in `require_relative'
  2: from /usr/lib/ruby/vendor_ruby/unicode/display_width/index.rb:3:in `<top (required)>'
  1: from /usr/lib/ruby/vendor_ruby/unicode/display_width/index.rb:4:in `<module:Unicode>'
/usr/lib/ruby/vendor_ruby/unicode/display_width/index.rb:5:in `<module:DisplayWidth>': undefined method `gunzip' for Gem:Module (NoMethodError)
```

The exit code was 1.

This error appears to be related to [this PR](https://github.com/janlelis/unicode-display_width/pull/15) where `Gem.gunzip` was replaced with `Gem::Util.gunzip`.

The warnings at the beginning of the output seem related to [this issue](https://github.com/rubygems/rubygems/issues/4702), though I don't think they are of consequence for this bug (but they are annoying).

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: rubocop 0.52.1+dfsg-1
Uname: Linux 5.10.0-051000-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.27
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Feb 4 12:57:53 2022
InstallationDate: Installed on 2021-01-04 (395 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: rubocop
UpgradeStatus: No upgrade log present (probably fresh install)