mod.md: correct some links
mod.md: correct some links

Change-Id: Ib0c4611c84c7eca652c6128faa8645be7c9ec9f0
Reviewed-on: https://go-review.googlesource.com/c/website/+/362034
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website