Unpin from requests 2.21.0

[kakoma]

Version 2.21.0 was released in 2018. Pinning the package to it creates dependency issues since other packages, such as urllib3, can't be updated past a certain version due to this constraint.

This PR opens this up to 2.2x since that picks newer versions but also steers clear of major updates. As of this writing, the latest version is 2.28.1

[raybesiga]

Excellent submission @kakoma a few issues from the CI report. Valid? CC @mossplix

[kakoma]

@raybesiga Thanks. I see this in the failure log:

src/mtnmomo/collection.py:56: in requestToPay
    "Ocp-Apim-Subscription-Key": super(Collection, self).config.collectionsKey
src/mtnmomo/config.py:80: in collectionsKey
    "COLLECTION_PRIMARY_KEY is missing in the configuration")

Haven't follow-through to see what's at the root of this but maybe the team might see something immediately, just looking at it? I'm not able to dig further into it at this point unfortunately

[raybesiga]

We no longer maintain this library but will see if I can get the requisite support in due course @kakoma