Change dependencies on requests

[pierresouchay]

The dependencies built in the lib do block the maximum version of requests and pytz as seen here:

https://github.com/aws/amazon-redshift-python-driver/blob/master/requirements.txt#L5

While it make perfect sense for major number, it forces the dependencies not to take into account minor patches, for instance, requests has a minor version 2.8.1, and this library is blocking us from using it.

Would you consider releasing those constraints?

example:

pytz>=2020.1
requests>=2.23.0,<2.29

[Brooke-white]

Hey @pierresouchay ,

thanks for reaching out with this inquiry. we can make this change apart of our next release, slated for mid/end August. thank you for brining this to our attention :)

[Brooke-white]

thanks for the pr, Pierre! I'll tag you in an update here once this is merged