fix: Error when using string key prefix as part of REDIS_URL

[joeyguerra]

BREAKING CHANGE: REDIS_URL should have the database number as the pathname instead of the prefix.

Example setting the key prefix via Redis URL: redis://localhost:6379/?prefix-for-redis-key or redis://localhost:6379?prefix-for-redis-key

fixes #58

[github-actions[bot]]

:tada: This PR is included in version 2.0.0 :tada:

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