Remove upper bound in dependency contraints

[SebCorbin]

Updated dependency version constraints to use '>=' instead of '^'.

Alternative

Use poetry-relax

References (taken from poetry-relax):

There's a lot to read on this topic! It's contentious and causing a lot of problems for maintainers and users.

The following blog posts by Henry Schreiner are quite comprehensive:

• Should You Use Upper Bound Version Constraints?
• Poetry Versions

Content from some members of the Python core developer team:

• Semantic Versioning Will Not Save You
• Why I don't like SemVer anymore
• Version numbers: how to use them?
• Versioning Software

Discussion and issues in the Poetry project:

• Please stop pinning to major versions by default, especially for Python itself
• Change default dependency constraint from ^ to >=
• Developers should be able to turn off dependency upper-bound calculations