code coverage dropped after the introduction of Set

See #166, release log:

• ad6cf45 by @yegor256: license badge
• f0c9f9b by @owtotwo: feat: impl Extend trait.
• e95b494 by @owtotwo: Merge branch 'yegor256:master'...
• 5ed2702 by @owtotwo: feat: Implemented (one by one)...
• 898d869 by @owtotwo: feat: add more methods for Set...
• 6c759b7 by @owtotwo: change: PartialEq and Eq can c...
• 6194a63 by @owtotwo: feat: add Set::intersection().
• 07e501f by @owtotwo: feat: add difference() method ...
• 9bbd9ed by @yegor256: typo
• 12d086f by @yegor256: Merge pull request #241 from y...
• 55d0cf3 by @rultor: new benchmark results
• 1ff59b2 by @owtotwo: test: add some test code lines...
• 1e2a141 by @rultor: new benchmark results
• 4a280b6 by @rultor: Merge branch '__rultor'
• 4f2b015 by @rultor: Merge branch '__rultor'
• b2c2f2c by @rultor: Merge branch '__rultor'
• 0ee95d6 by @renovate[bot]: chore(deps): update rust crate...
• 5956f0a by @renovate[bot]: chore(deps): update rust crate...
• ea78e25 by @renovate[bot]: fix(deps): update rust crate s...
• 971de73 by @renovate[bot]: chore(deps): update rust crate...
• and 157 more...

Released by Rultor 2.0-SNAPSHOT, see build log