Update base64 requirement from 0.21.0 to 0.22.1

[dependabot]

Updates the requirements on base64 to permit the latest version.

Changelog

Sourced from base64's changelog.

0.22.1

• Correct the symbols used for the predefined alphabet::BIN_HEX.

0.22.0

• DecodeSliceError::OutputSliceTooSmall is now conservative rather than precise. That is, the error will only occur if the decoded output cannot fit, meaning that Engine::decode_slice can now be used with exactly-sized output slices. As part of this, Engine::internal_decode now returns DecodeSliceError instead of DecodeError, but that is not expected to affect any external callers.
• DecodeError::InvalidLength now refers specifically to the number of valid symbols being invalid (i.e. len % 4 == 1), rather than just the number of input bytes. This avoids confusing scenarios when based on interpretation you could make a case for either InvalidLength or InvalidByte being appropriate.
• Decoding is somewhat faster (5-10%)

0.21.7

• Support getting an alphabet's contents as a str via Alphabet::as_str()

0.21.6

• Improved introductory documentation and example

0.21.5

• Add Debug and Clone impls for the general purpose Engine

0.21.4

• Make encoded_len const, allowing the creation of arrays sized to encode compile-time-known data lengths

0.21.3

• Implement source instead of cause on Error types
• Roll back MSRV to 1.48.0 so Debian can continue to live in a time warp
• Slightly faster chunked encoding for short inputs
• Decrease binary size

0.21.2

• Rollback MSRV to 1.57.0 -- only dev dependencies need 1.60, not the main code

0.21.1

• Remove the possibility of panicking during decoded length calculations
• DecoderReader no longer sometimes erroneously ignores padding #226

Breaking changes

• Engine.internal_decode return type changed
• Update MSRV to 1.60.0

0.21.0

... (truncated)

Commits

• e144006 v0.22.1
• 64cca59 Merge pull request #271 from JobanSD/patch-1
• 838355e Correct BinHex 4.0 alphabet according to specifications
• bf15ccf Merge pull request #270 from marshallpierce/mp/clippy
• fc6aabe Appease clippy
• 9a518a2 Merge pull request #267 from bdura/patch-1
• d96c80f Merge branch 'marshallpierce:master' into patch-1
• 5d70ba7 Merge pull request #269 from marshallpierce/mp/decode-precisely
• efb6c00 Release notes
• 2b91084 Add some tests to boost coverage
• Additional commits viewable in compare view

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