[DOC] Tweaks for StringIO#gets #548

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.0	1m 7s
windows-latest mingw	56s
windows-latest 2.7	1m 30s
windows-latest 3.1	1m 5s
windows-latest 3.2	58s
windows-latest 3.4	1m 4s
windows-latest 3.3	58s
windows-latest mswin	1m 8s
windows-latest jruby-head	1m 54s
	10m 45s

Provide feedback