Updates doc by running these commands:
- mksyntaxgo from the google/re2 repo, which changes comment according
to https://golang.org/s/generatedcode
- gofmt -w regexp/syntax/doc.go
Change-Id: I66a9dd9fa841cbce899ab3aa32d7face798d2920
Reviewed-on: https://go-review.googlesource.com/c/go/+/572275
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com>