builtin: mention PanicNilError in comments of recover
As of CL 461956 `recover` will not return `nil` if `panic` is called with `nil`. I have updated comments of `recover` to account for this change.
Change-Id: Ibd0b27fe9b89fb29349b62ad34e762239a1d165b
GitHub-Last-Rev:
c773abb75c8cd8e08c3470f064a3205573156fea
GitHub-Pull-Request: golang/go#64393
Reviewed-on: https://go-review.googlesource.com/c/go/+/544975
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>