title: make virtualenv with specific python version(MACOS)
body: <p>I installed brew, python3 (default and latest version) and pip3, pyenv.</p>
  
  <p>TensorFlow does not support python3.7 now, so I heard that I should make a virtualenv that runs 3.6 or lower version independently.</p>
  
  <p>I installed python 3.6.7 by <code>pyenv install 3.6.7</code> but can't make <code>virtualenv -p 3.6.7 (mydir)</code> because 3.6.7 is not in the <code>PATH</code> (<code>usr/local/bin</code>).</p>
  
  <p>How can I update my <code>PATH</code>?</p>