Change an instance of default_features in Cargo.toml to default-features

[LikeLakers2]

As per cargo itself when running a cargo build:

default_features is deprecated in favor of default-features and will not work in the 2024 edition (in the quickcheck dependency)

Since default_features and default-features work the same, this should not change any functionality beyond removing the warning when building itertools. To be sure, however, I ran cargo test after the change, and all tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.35%. Comparing base (6814180) to head (3d7037e).
Report is 127 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #985 +/- ## ========================================== - Coverage 94.38% 94.35% -0.04%  ========================================== Files 48 49 +1 Lines 6665 6768 +103 ========================================== + Hits 6291 6386 +95  - Misses 374 382 +8 

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[jswrenn]

Thanks!