title: Upgrade pip to latest version
body: <p>In one environment (<code>Ubuntu 20.04.4 LTS</code>), I get this:</p>
  <pre><code>» pip --version
  pip 21.3.1 from /xxx/.venv/lib/python3.6/site-packages/pip (python 3.6)
  
  » pip install --upgrade pip
  Requirement already satisfied: pip in ./.venv/lib/python3.6/site-packages (21.3.1)
  </code></pre>
  <p>In another environment (docker container running <code>CentOS Linux release 7.9.2009 (Core)</code>), I get this:</p>
  <pre><code>» pip install --upgrade --no-cache-dir pip
  Collecting pip                                
    Downloading https://files.pythonhosted.org/packages/a4/6d/6463d49a933f547439d6b5b98b46af8742cc03ae83543e4d7688c2420f8b/pip-21.3.1-py3-none-any.whl (1.7MB)
      100% |████████████████████████████████| 1.7MB 11.3MB/s 
  Installing collected packages: pip                                                                                                 
    Found existing installation: pip 9.0.3
      Uninstalling pip-9.0.3:                                                                                                        
        Successfully uninstalled pip-9.0.3                                                                                           
  Successfully installed pip-21.3.1
  You are using pip version 21.3.1, however version 22.0.4 is available.                   
  You should consider upgrading via the 'pip install --upgrade pip' command.                                   
  </code></pre>
  <p>Two questions:</p>
  <ol>
  <li>Why does one environment detect <code>21.3.1</code> as the newest <code>pip</code> version, and the other environment detects <code>22.0.4</code>? As of this writing, <a href="https://pypi.org/project/pip/" rel="nofollow noreferrer">PyPi</a> has <code>22.0.4</code></li>
  <li>Why does the environment that detects <code>22.0.4</code> as the latest <code>pip</code> version does not use that version for installation? I am telling it to upgrade to the latest version!</li>
  </ol>