text: Title: Requests missing from dependencies
  Body: This is what I ran into when trying out `shillelagh` in a bare virtual environment:
  
  ```
    File "/Users/mrshu/.local/share/virtualenvs/shillelagh-example-NzrXhpJb/lib/python3.9/site-packages/shillelagh/backends/apsw/dialects/gsheets.py", line 12, in <module>
      import requests
  ModuleNotFoundError: No module named 'requests'
  ````
  
  @betodealmeida would you be up for adding `requests` as one of the requirements?
  
  Thanks!