Update drf_social_oauth2 version to 2.2.1

[wagnerdelima]

This commit updates the version of drf_social_oauth2 package in multiple files including __init__.py and conf.py. Also, the installation instruction in the documentation has been updated to reflect the new released version.

Description

Please include changes' summary that your pull request entails.

Fixes # (issue)

Checklist

• [ ] Do unit tests run with no errors?
• [ ] Has coverage not decreased?
• [ ] Is your code concise and clean?
• [ ] Are the conf.py and installation sphinx updated with the new version?
• [ ] Is the init.py version variable updated?