[skfe] Fix deploy_new_certs.sh to use rubberstamper.
[skfe] Fix deploy_new_certs.sh to use rubberstamper.

Change-Id: Iae8d2896e9e2383b72fe88c282c3ed6dd35d37d0
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/487225
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot