go/analysis/singlechecker: fix whitespace in package documentation
go/analysis/singlechecker: fix whitespace in package documentation

Consistent whitespace makes godoc render the snippet without
extraneous leading indentation.

Change-Id: If7b6910cd431ada0db0f59b7aecc9e5bd011af23
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266877
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Dominik Honnef <aeacd46bb4fd3f59504c7762d9af6bd04f20aa1f@honnef.co>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools