title: Docker image defaults to python 3.6 even though I install python 3.7
body: <p>I'm trying to set up a Docker image based on Ubuntu 18.04 that runs some code with Python 3.7</p>
  
  <p>The dockerfile specifically mentions installing python 3.7 but in the image binary folder there is also python 3.6 that the image uses as default and which I don't even need.</p>
  
  <p>What change would I need to make in order to only have python 3.7 on the image?</p>
  
  <p>The dockerfile currently looks like this:</p>
  
  <pre><code>FROM ubuntu:18.04
  
  #format changes required for asammdf v3.4.0
  ENV LANG C.UTF-8
  ENV LC_ALL C.UTF-8
  
  #install python 3.7 and pip
  RUN apt-get update &amp;&amp; apt-get install -y \
      python3.7 \
      python3-pip
  
  #set main entry point as working directory
  WORKDIR /
  
  RUN pip3 install --upgrade setuptools
  
  RUN alias python3=/usr/bin/python3.7
  RUN pip3 install -r requirements.txt
  
  </code></pre>
  
  <p>Later details:</p>
  
  <p>Added the <code>alias</code> command hoping that it would work but it seems to be ignored in the dockerfile, the execution still goes to python3.6</p>
  
  <p>The requirements installation works fine but installs all packages in the 3.6 directory so even if I manually use the python3.7 execution while in the container, it doesn't see the installed modules</p>