build

Drop support for Ruby prior to 3.1 #28

Job	Run time
lint	10s
test (macos-latest, 3.1)	23s
test-vendor (macos-latest, 3.1, vendor/github.com/twbs/bootstrap)	16s
test (macos-latest, 3.2)	20s
test-vendor (macos-latest, 3.2, vendor/github.com/twbs/bootstrap)	17s
test (macos-latest, 3.3)	20s
test-vendor (macos-latest, 3.3, vendor/github.com/twbs/bootstrap)	23s
test (macos-latest, ruby)	1m 27s
test-vendor (macos-latest, ruby, vendor/github.com/twbs/bootstrap)	17s
test (macos-latest, jruby)	2m 42s
test-vendor (macos-latest, jruby, vendor/github.com/twbs/bootstrap)	1m 41s
test (ubuntu-latest, 3.1)	14s
test-vendor (ubuntu-latest, 3.1, vendor/github.com/twbs/bootstrap)	7s
test (ubuntu-latest, 3.2)	9s
test-vendor (ubuntu-latest, 3.2, vendor/github.com/twbs/bootstrap)	8s
test (ubuntu-latest, 3.3)	7s
test-vendor (ubuntu-latest, 3.3, vendor/github.com/twbs/bootstrap)	9s
test (ubuntu-latest, ruby)	11s
test-vendor (ubuntu-latest, ruby, vendor/github.com/twbs/bootstrap)	8s
test (ubuntu-latest, jruby)	46s
test-vendor (ubuntu-latest, jruby, vendor/github.com/twbs/bootstrap)	40s
test (windows-latest, 3.1)	1m 17s
test-vendor (windows-latest, 3.1, vendor/github.com/twbs/bootstrap)	1m 21s
test (windows-latest, 3.2)	1m 57s
test-vendor (windows-latest, 3.2, vendor/github.com/twbs/bootstrap)	1m 53s
test (windows-latest, 3.3)	1m 24s
test-vendor (windows-latest, 3.3, vendor/github.com/twbs/bootstrap)	1m 16s
test (windows-latest, ruby)	1m 36s
test-vendor (windows-latest, ruby, vendor/github.com/twbs/bootstrap)	1m 18s
	22m 57s

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