title: Can't update RubyGems or install RubyGems from source
body: <p>When I attempt to run <code>sudo update_rubygems</code> or <code>sudo gem update --system</code> I get similar errors:</p>
  <pre><code>Installing RubyGems 3.2.3
  Traceback (most recent call last):
          4: from setup.rb:23:in `&lt;main&gt;'
          3: from setup.rb:23:in `require'
          2: from /var/lib/gems/2.5.0/gems/rubygems-update-3.2.3/lib/rubygems.rb:1348:in `&lt;top (required)&gt;'
          1: from /var/lib/gems/2.5.0/gems/rubygems-update-3.2.3/lib/rubygems.rb:1348:in `require'
  /usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:43:in `&lt;top (required)&gt;': uninitialized constant Gem::BasicSpecification (NameError)
  </code></pre>
  <p>I've tried reinstalling RubyGems 3.2.3 from source using <code>ruby setup.rb</code> and I get essentially the same error.</p>
  <pre><code>Traceback (most recent call last):
          4: from setup.rb:23:in `&lt;main&gt;'
          3: from setup.rb:23:in `require'
          2: from /home/izaguirrejoe/Downloads/rubygems-3.2.3/lib/rubygems.rb:1348:in `&lt;top (required)&gt;'
          1: from /home/izaguirrejoe/Downloads/rubygems-3.2.3/lib/rubygems.rb:1348:in `require'
  /usr/lib/ruby/vendor_ruby/rubygems/defaults/operating_system.rb:43:in `&lt;top (required)&gt;': uninitialized constant Gem::BasicSpecification (NameError)
  </code></pre>
  <p>One clue: I'm a noob and I ran <code>sudo apt-get autoremove</code> and it removed a bunch of Ruby-looking stuff. Maybe that was it? I did that, updated Vim to the newest version and installed YouCompleteMe, and now my existing rails app is not working. New rails apps work just fine, but I'd like to be able to update RubyGems. I'm on the verge of just reinstalling Debian and starting over, this is frustrating.</p>
  <p>Another clue: hours of research has revealed that I may have two versions of Ruby installed. When I run <code>which -a ruby</code> I get</p>
  <pre><code>/usr/bin/ruby
  /bin/ruby
  </code></pre>