Relax async dependency version requirement

[zhulik]

As async-redis perfectly works with async 2.0 it does not make any sense to depend on the old version only

Closes #41

Types of Changes

• Maintenance.

Testing

• [ ] I added tests for my changes.
• [X] I tested my changes locally.
• [ ] I tested my changes in staging.
• [ ] I tested my changes in production.

[zhulik]

@ioquatix could you please also draft a new release if it's merged