title: No matching distribution found for django==3.0 on Ubuntu 16.04
body: <p>I just reinstalled Ubuntu 16.04, then made a virtualenv and tried to install Django with</p>
  
  <pre><code>sudo pip3 install django==3.0
  </code></pre>
  
  <p>but this generated the following error:</p>
  
  <pre><code>ERROR: Could not find a version that satisfies the requirement django==3.0 
  (from versions: 1.1.3, 1.1.4, 1.2, 1.2.1, 1.2.2, 1.2.3, 1.2.4, 1.2.5,
   1.2.6, 1.2.7, 1.3, 1.3.1, 1.3.2, 1.3.3, ...  2.2.5, 2.2.6, 2.2.7, 2.2.8, 2.2.9)
  ERROR: No matching distribution found for django==3.0
  </code></pre>
  
  <p>After searching, I think my <code>pip</code> version is too low, so it doesn't know about the new versions of Django. I tried to upgrade <code>pip</code> with</p>
  
  <pre><code>sudo pip install --upgrade pip
  </code></pre>
  
  <p>but this gave</p>
  
  <pre><code>WARNING: The directory '/home/hugh/.cache/pip' or 
  its parent directory is not owned or is not writable by the current user. 
  The cache has been disabled. Check the permissions and owner of that directory. 
  If executing pip with sudo, you may want sudo's -H flag.
  Requirement already up-to-date: pip in /usr/local/lib/python3.5/dist-packages (20.0.2)
  </code></pre>
  
  <p>and I know that the <code>pip</code>'s lastest version is 20.0.2.</p>
  
  <p>Why can't I install Django version 3.0?</p>