Update digital-ocean-spaces.rst

The vars listed didn't work for Digital Ocean so I wrote the values that worked for me and removed the following from the docs:

region_name
endpoint_url
access_key
secret_key

docs/backends/s3_compatible/digital-ocean-spaces.rst

@@ -3,6 +3,6 @@ Digital Ocean
 
 Digital Ocean Spaces implements the S3 protocol. To use it follow the instructions in the :doc:`Amazon S3 docs <../amazon-S3>` with the important caveats that you must:
 
-- Set ``region_name`` to your Digital Ocean region (such as ``nyc3`` or ``sfo2``)
-- Set ``endpoint_url`` to the value of ``https://${region_name}.digitaloceanspaces.com``
-- Set the values of ``access_key`` and ``secret_key`` to the corresponding values from Digital Ocean
+- Set ``AWS_S3_REGION_NAME`` to your Digital Ocean region (such as ``nyc3`` or ``sfo2``)
+- Set ``AWS_S3_ENDPOINT_URL`` to the value of ``https://${region_name}.digitaloceanspaces.com``
+- Set the values of ``AWS_ACCESS_KEY_ID`` and ``AWS_SECRET_ACCESS_KEY`` to the corresponding values from Digital Ocean