title: how to add "json" library in heroku, also for "time"
body: <p>i'm trying to deploy to heroku a python app but terminal outputs the message:</p>
  <pre><code>remote:        ERROR: Could not find a version that satisfies the requirement json==3 (from -r /tmp/build_b339be1c/requirements.txt (line 3)) (from versions: none)
  remote:        ERROR: No matching distribution found for json==3 (from -r /tmp/build_b339be1c/requirements.txt (line 3))
  </code></pre>
  <p>my requirements.txt:</p>
  <pre><code>vk_api
  requests
  json
  time
  </code></pre>
  <p>my runtime.txt: python-3.6.15</p>