Add specs for reserved keywords #1726

Job	Run time
RuboCop	26s
specs (ubuntu, 3.0.6)	1m 46s
specs (ubuntu, 3.1.4)	1m 33s
specs (ubuntu, 3.2.2)	1m 32s
specs (ubuntu, 3.3.0)	1m 24s
specs (macos, 3.0.6)	1m 53s
specs (macos, 3.1.4)	1m 35s
specs (macos, 3.2.2)	1m 9s
specs (macos, 3.3.0)	1m 37s
specs (windows, 3.0.6)	4m 50s
specs (windows, 3.1.4)	4m 10s
specs (windows, 3.2.2)	4m 32s
specs (windows, 3.3.0)	3m 55s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 30s
	31m 52s

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