title: Unable to downgrade version of Python package by `pip install -I`
body: <p>To temporary workaround a compatibility issue, I tried to downgrade version of Python package <code>arrow</code> from 0.17.0 to 0.13.2.</p>
  <p>On a particular server I was unable to, as the below command calls to install 0.13.2 but ends up install back 0.17.0. If remove the virtual environment, and generate a new one and freshly install 0.13.2, it works OK.</p>
  <p>I also tested on a virtual machine, and the downgrade works OK without this symptom.</p>
  <p>I'm wondering why, and any inputs will be highly appreciated.</p>
  <pre><code>(venv3.7) [user@host freeze]$ pip install -I arrow==0.13.2
  Collecting arrow==0.13.2
    Using cached arrow-0.13.2-py2.py3-none-any.whl (37 kB)
  Collecting python-dateutil
    Using cached python_dateutil-2.8.1-py2.py3-none-any.whl (227 kB)
  Collecting six&gt;=1.5
    Using cached six-1.15.0-py2.py3-none-any.whl (10 kB)
  Installing collected packages: six, python-dateutil, arrow
  Successfully installed arrow-0.17.0 python-dateutil-2.8.1 six-1.15.0
  (venv3.7) [user@host freeze]$
  </code></pre>