cmd/relnote: ignore unmerged CLs
cmd/relnote: ignore unmerged CLs

Change-Id: Ie76e8c11663b0092bae5f842d40e81b964e767d0
Reviewed-on: https://go-review.googlesource.com/45781
Reviewed-by: Matt Layher <76528ff2e917253aa2211f68e4ca60b5b846dcf5@gmail.com>
Run-TryBot: Matt Layher <76528ff2e917253aa2211f68e4ca60b5b846dcf5@gmail.com>

golang/build,golang/build,golang/build,golang/build