Fix typo in go_branch.sh script.
Fix typo in go_branch.sh script.

With the ticks, the command `master` is actually be run and the output included
(which is nothing). This is confusing, as we actually mean to say "master" in
the description of the Go branch.

PiperOrigin-RevId: 282426081

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor