v0.21.3

Enhancements

• Add config no_short_urls and env var HEX_NO_SHORT_URLS to disable short URL generation
• Mention mix hex.sponsor when fetching packages that accept sponsorship
• Add --key option to mix hex.repo show NAME to print repository key
• Improve output when update check fails
• Print hint if version resolution is slow

Bug fixes

• Improve version backtracking to fix slow version resolutions and downgrading of dependencies