[DOC] Tweaks for StringIO#binmode (#147) #436

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.1	1m 57s
windows-latest 3.0	1m 7s
windows-latest 3.3	2m 22s
windows-latest 2.7	1m 46s
windows-latest 3.2	2m 10s
windows-latest jruby-head	1m 43s
windows-latest mswin	1m 1s
windows-latest 3.4	1m 3s
windows-latest mingw	57s
	14m 11s

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