internal/worker: update static worker path
internal/worker: update static worker path

CL 359395 updated dochtml.LoadTemplates to expect a static path relative
to /doc. This CL updates the path to fix the worker.

Change-Id: If1562e786112f5d00daa6d083ed24709499d1bce
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/360434
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

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