title: How to change default user for psql command
body: <p>When I run the command 'heroku pg:psql' it tries to authenticate me under 'justinwong'. This is a problem because that is not a user in the list of roles when I run \du command in postgres.</p>
  
  <p>The only user that exists should be postgres.</p>
  
  <p>How do I modify the default user that the 'heroku pg:psql' or 'psql' command tries to log me in with so that it's postgres rather than justinwong?</p>