title: Serverless deploy with serverless-python-requirements does not work
body: <p>I am trying to deploy a python lambda function using serverless. I need the psycopg2 library so I used the serverless-python-requirements plugin and added it to my serverless.yml file. </p>
  
  <pre><code>plugins:
    - serverless-python-requirements
  custom:
      pythonRequirements:
          dockerizePip: non-linux
  </code></pre>
  
  <p>I can deploy the function successfully:</p>
  
  <pre><code>Serverless: Installing requirements from 
  /Users/Desktop/postgresql/.serverless/requirements/requirements.txt ...
  Serverless: Docker Image: lambci/lambda:build-python3.6
  Serverless: Packaging service...
  Serverless: Excluding development dependencies...
  Serverless: Injecting required Python packages to package...
  Serverless: Uploading CloudFormation file to S3...
  Serverless: Uploading artifacts...
  Serverless: Uploading service .zip file to S3 (43.07 MB)...
  Serverless: Validating template...
  Serverless: Updating Stack...
  Serverless: Checking Stack update progress...
  
  ..............
  Serverless: Stack update finished...
  </code></pre>
  
  <p>But when I check my Cloudwatch logs, it says that there is "No module named 'psycopg2' ". </p>
  
  <p>The structure of my zip file is: </p>
  
  <pre><code>    |--node_modules
      |--.gitignore
      |--handler.py
      |--package-lock.json
      |--package.json
      |--serverless.yml
  </code></pre>
  
  <p>No .serverless/ dir was created when I ran serverless deploy...</p>
  
  <p>Any help would be greatly appreciated!</p>