title: Heroku is using the wrong requirements.txt when I try to git push my app
body: <p>I'm trying to install a django app to Heroku for the first time.  I've been following tutorials and things were going fine until <code>git push heroku master</code>.  I get an error with postgrequl/psycopg2:</p>
  
  <pre><code>Collecting psycopg2==2.6.2 (from -r /tmp/build_9a1b9401a05f6186e32ef1f993bdd183/requirements.txt (line 10))
  remote:          Downloading blah...blah../bc/psycopg2-2.6.2.tar.gz (376kB)
  remote:            Complete output from command python setup.py egg_info:
  remote:            running egg_info
  remote:            creating pip-egg-info/psycopg2.egg-info
  remote:            writing pip-egg-info/psycopg2.egg-info/PKG-INFO
  remote:            writing dependency_links to pip-egg-info/psycopg2.egg-info/dependency_links.txt
  remote:            writing top-level names to pip-egg-info/psycopg2.egg-info/top_level.txt
  remote:            writing manifest file 'pip-egg-info/psycopg2.egg-info/SOURCES.txt'
  remote:            Error: could not determine PostgreSQL version from '10.5'
  remote:
  remote:            ----------------------------------------
  remote:        Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-mu5yzi1s/psycopg2/
  remote:  !     Push rejected, failed to compile Python app.
  remote:
  remote:  !     Push failed
  remote: Verifying deploy...
  remote:
  remote: !       Push rejected to django-randomizer.
  </code></pre>
  
  <p>I did some searches and I read where other people had problems because they had an older version of psycopg2.  So I edited my requirements.txt file to include <code>psycopg2-2.7.5</code>, which is the latest.  I think try `git push heroku master' again and I get the same error. The error references psycopg2-2.6.2.</p>
  
  <p>I even deleted my app and started again, but when it came to the git push, I get the same error. At this time I think that git is in some state where it keeps trying to do the push that already failed. I'm not sure though.  Any ideas?</p>
  
  <pre><code>git reflog:
  5fd142e (HEAD -&gt; deployheroku, origin/deployheroku) HEAD@{0}: pull origin deployheroku: Fast-forward
  df048a9 (origin/master, origin/HEAD, master) HEAD@{1}: reset: moving to HEAD^
  5fd142e (HEAD -&gt; deployheroku, origin/deployheroku) HEAD@{2}: commit: change settings and wsgi for heroku
  df048a9 (origin/master, origin/HEAD, master) HEAD@{3}: checkout: moving from master to deployheroku
  df048a9 (origin/master, origin/HEAD, master) HEAD@{4}: commit: restore local version
  873d636 HEAD@{5}: commit: updated psycopg2 in requirements.txt
  aebfe43 HEAD@{6}: commit: get files ready for heroku
  6273553 HEAD@{7}: commit: removed old files
  9b2c347 HEAD@{8}: commit: update with new app name
  6b4103d HEAD@{9}: clone: from https://github.com/shmish/django-randomizer.git
  </code></pre>
  
  <p>My requirements.txt is:</p>
  
  <pre><code>certifi==2018.8.13
  chardet==3.0.4
  defusedxml==0.5.0
  Django==2.0.8
  django-allauth==0.36.0
  django-filter==2.0.0
  docopt==0.6.2
  idna==2.7
  oauthlib==2.1.0
  psycopg2==2.7.5
  python-decouple==3.1
  python3-openid==3.1.0
  pytz==2018.5
  requests==2.19.1
  requests-oauthlib==1.0.0
  urllib3==1.23
  whitenoise==4.0
  yarg==0.1.9
  </code></pre>