Bump nio4r from 2.5.1 to 2.5.4

[dependabot-preview]

Bumps nio4r from 2.5.1 to 2.5.4.

Changelog

Sourced from nio4r's changelog.

2.5.4 (2020-09-16)

• #251 Intermittent SEGV during GC. ([@boazsegev])

2.5.3 (2020-09-07)

• #241 Possible bug with Ruby >= 2.7.0 and GC.compact. ([@boazsegev])

2.5.2 (2019-09-24)

• #220 Update to libev-4.27 & fix assorted warnings. ([@ioquatix])

• #225 Avoid need for linux headers. ([@ioquatix])

2.4.0 (2019-07-07)

• #211 Enable KQUEUE on macOS 10.14+. ([@ioquatix])

• Bump minimum supported Ruby to 2.3. ([@ioquatix])

• Assorted fixes for TruffleRuby & JRuby. ([@eregon], [@olleolleolle]) Possible bug with Ruby >= 2.7.0 and GC.compact

• Update libev to v4.25. ([@ioquatix])

• Bind to ephemeral (port 0) for more reliable specs. ([@ioquatix])

• Improve handling of SSL sockets and related specs. ([@MSP-Greg])

2.3.1 (2018-05-03)

• #188 Fix remove interests ([@ioquatix])

2.3.0 (2018-03-15)

Commits

• 40de869 Prepare for v2.5.4 release.
• 78b9d89 Remove unneeded assertions.
• a0054f0 Update ext/nio4r/monitor.c
• 1ccd5a0 replace if with assert, keep memory init.
• 0d6adaf actually, initialize the whole memory block to zero
• f6b1810 test allocation for failure and initialize memory
• cd52113 Add if statement, even if redundant
• 5baa5ed README.md: update build status badge
• bc5e5b6 Move EV_STANDALONE definition to extconf.rb (#250)
• 77f859a Add space between control statements and brackets.
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #284.