Typo fix: underscoes => underscores #385

Job	Run time
RuboCop	33s
specs (ubuntu, 3.1.6)	1m 32s
specs (ubuntu, 3.2.7)	1m 25s
specs (ubuntu, 3.3.7)	1m 29s
specs (ubuntu, 3.4.2)	1m 33s
specs (macos, 3.1.6)	1m 18s
specs (macos, 3.2.7)	1m 30s
specs (macos, 3.3.7)	1m 27s
specs (macos, 3.4.2)	1m 37s
specs (windows, 3.1.6)	3m 50s
specs (windows, 3.2.7)	4m 0s
specs (windows, 3.3.7)	4m 54s
specs (windows, 3.4.2)	4m 0s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 28s
	30m 36s

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