Merge pull request #1147 from nobu/date_specs #1594

Job	Run time
RuboCop	26s
specs (ubuntu, 3.0.6)	1m 28s
specs (ubuntu, 3.1.4)	1m 29s
specs (ubuntu, 3.2.2)	1m 23s
specs (ubuntu, 3.3.0)	1m 22s
specs (macos, 3.0.6)	2m 0s
specs (macos, 3.1.4)	1m 43s
specs (macos, 3.2.2)	1m 42s
specs (macos, 3.3.0)	2m 2s
specs (windows, 3.0.6)	3m 16s
specs (windows, 3.1.4)	4m 26s
specs (windows, 3.2.2)	4m 29s
specs (windows, 3.3.0)	3m 58s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 22s
	31m 6s

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