internal/fetch: add another known alternative module
internal/fetch: add another known alternative module

Change-Id: Iae9a649918d165ac36972fe784728ce341d41871
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/400359
Run-TryBot: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Reviewed-by: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>

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