Fix Rubocop warnings #2065

Job	Run time
RuboCop	1m 6s
specs (macos, 3.3.8)	1m 18s
specs (ubuntu, 3.4.4)	1m 36s
specs (ubuntu, 3.2.8)	1m 30s
specs (macos, 3.2.8)	1m 18s
specs (ubuntu, 3.3.8)	1m 28s
specs (macos, 3.4.4)	4m 16s
specs (ubuntu, 3.4.4, --enable-frozen-string-literal)	1m 38s
specs (windows, 3.2.8)	3m 7s
specs (windows, 3.3.8)	3m 9s
specs (ubuntu, 3.4.4, --parser=parse.y)	1m 39s
specs (windows, 3.4.4)	3m 6s
	25m 11s

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