Simplify version requirement in bin/rubocop #1770

Job	Run time
RuboCop	31s
specs (ubuntu, 3.0.6)	1m 35s
specs (ubuntu, 3.1.4)	1m 32s
specs (ubuntu, 3.2.2)	1m 27s
specs (ubuntu, 3.3.0)	1m 30s
specs (macos, 3.0.6)	1m 35s
specs (macos, 3.1.4)	1m 21s
specs (macos, 3.2.2)	1m 35s
specs (macos, 3.3.0)	1m 23s
specs (windows, 3.0.6)	3m 42s
specs (windows, 3.1.4)	5m 33s
specs (windows, 3.2.2)	4m 38s
specs (windows, 3.3.0)	5m 36s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 29s
	33m 27s

Provide feedback