title: No module named 'requests_toolbelt'
body: <p>So, I'm trying to upload my python app to heroku but when I use a script with 'requests_toolbelt' it says is not found.</p>
  
  <p>Here my log:</p>
  
  <pre><code>Traceback (most recent call last):
    File "girl.py", line 12, in &lt;module&gt;
      from Coffe import CoffeAPI
    File "/app/CoffeAPI/__init__.py", line 29, in &lt;module&gt;
      from requests_toolbelt import MultipartEncoder
  ImportError: No module named 'requests_toolbelt'
  </code></pre>
  
  <p>Here my requeriments.txt:</p>
  
  <pre><code>requests-toolbelt==0.7.1
  moviepy==0.2.2.11
  requests==2.13.0
  </code></pre>
  
  <p>Do I need an specific buildpack to run 'requests_toolbelt'?</p>