deploy: add update-traffic command to frontend deploy
deploy: add update-traffic command to frontend deploy

To match the private repo, added an additional step to the
public deploy script.

Change-Id: I5f5a9eae698318e0777ff1223dff3a3305be132a
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/367594
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite