Bump up 3.1.1 #175

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (2.5 / ubuntu-latest)	25s
build (2.5 / windows-latest)	4m 12s
build (2.6 / ubuntu-latest)	30s
build (2.6 / macos-latest)	32s
build (2.6 / windows-latest)	2m 9s
build (2.7 / ubuntu-latest)	26s
build (2.7 / macos-latest)	29s
build (2.7 / windows-latest)	6m 15s
build (3.0 / ubuntu-latest)	21s
build (3.0 / macos-latest)	23s
build (3.0 / windows-latest)	2m 37s
build (3.1 / ubuntu-latest)	21s
build (3.1 / macos-latest)	20s
build (3.1 / windows-latest)	1m 6s
build (3.2 / ubuntu-latest)	15s
build (3.2 / macos-latest)	15s
build (3.2 / windows-latest)	5m 32s
build (3.3 / ubuntu-latest)	19s
build (3.3 / macos-latest)	30s
build (3.3 / windows-latest)	3m 22s
build (head / ubuntu-latest)	12s
build (head / macos-latest)	16s
build (truffleruby-head / ubuntu-latest)	32s
build (truffleruby-head / macos-latest)	32s
build (mswin / windows-latest)	2m 5s
build (mingw / windows-latest)	1m 58s
	35m 58s

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