blog: fix incorrect anchor href

Updates link to 'pseudo-version' documentation from
'cmd/go/#hdr-Pseudo_versions' to 'ref/mod#pseudo-versions'.

Change-Id: I67843580c07cff082858cc85cd768290a0aa8f37
Reviewed-on: https://go-review.googlesource.com/c/website/+/578655
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
diff --git a/_content/blog/using-go-modules.md b/_content/blog/using-go-modules.md
index f104f0e..f953e0c 100644
--- a/_content/blog/using-go-modules.md
+++ b/_content/blog/using-go-modules.md
@@ -228,7 +228,7 @@
 
 The `golang.org/x/text` version `v0.0.0-20170915032832-14c0d48ead0c`
 is an example of a
-[pseudo-version](/cmd/go/#hdr-Pseudo_versions),
+[pseudo-version](/ref/mod#pseudo-versions),
 which is the `go` command's version syntax
 for a specific untagged commit.