title: "PACKAGES DO NOT MATCH THE HASHES" error with pip
body: <p>I'm trying to install packages using pip. In this case for OpenCV. However, I'm unable to install anything. I'm using python 3.5.3 en pip 18.0 (installed using get-pip.py). </p>
  
  <p>Whatever I try, the command 'pip install package-name' generates the following error:</p>
  
  <blockquote>
    <p>THESE PACKAGES DO NOT MATCH THE HASHES FROM THE REQUIREMENTS FILE. If you have updated the package versions, please update the hashes. Otherwise, examine the package contents carefully; someone may have tampered with them.
        opencv-contrib-python-headless from <a href="https://www.piwheels.org/simple/opencv-contrib-python-headless/opencv_contrib_python_headless-3.4.3.18-cp35-cp35m-linux_armv6l.whl#sha256=ff894c0cc7c98b05b7b260a1dc462e7ad0a4220b042072fc0134a2b7a92bc4a5" rel="noreferrer">https://www.piwheels.org/simple/opencv-contrib-python-headless/opencv_contrib_python_headless-3.4.3.18-cp35-cp35m-linux_armv6l.whl#sha256=ff894c0cc7c98b05b7b260a1dc462e7ad0a4220b042072fc0134a2b7a92bc4a5</a>:
            Expected sha256 ff894c0cc7c98b05b7b260a1dc462e7ad0a4220b042072fc0134a2b7a92bc4a5
                 Got        4119d8c56d19ef044c1faca317dd10f2bb3b50cbee77426a22feca9b641c5637</p>
  </blockquote>
  
  <p>Things I've tried:</p>
  
  <ul>
  <li>using '--no-cache-dir' as suggested by another using having the same question.</li>
  <li>reinstalling python/pip or trying other versions of python.</li>
  </ul>