Update env_logger requirement from 0.7.1 to 0.8.4

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Updates the requirements on env_logger to permit the latest version.

Release notes

Sourced from env_logger's releases.

0.8.4

Improvements:

• Allow writing logs to a custom output target (via Target::Pipe)

Bug fixes:

• Actually allow overriding filter levels using env_logger::Builders methods, as documented

Commits

• 13cafce Bump version to 0.8.4
• 0900811 Ensure unique directive names when building filters
• 1a8379a Allow writing logs to a custom output target (Target::Pipe)
• 2151771 Upgrade to GitHub-native Dependabot
• 16d982e Fix lints
• 67adcba Re-add tests to the crates.io tarball
• c9f033d Release version 0.8.3
• eed1651 Only include necessary files in crates.io tarballs
• 664ca1a Don't deny(warnings)
• 8ef1615 Merge pull request #192 from jthacker/feat/custom-suffix
• Additional commits viewable in compare view

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