internal/dl: redirect to downloadBaseURL for GPG signatures

Fixes golang/go#35717

Change-Id: I6d063fb1d6c33b60a7bcf34cda832011a2fc120d
GitHub-Last-Rev: 9706ecb20d608d8688f4cf5dfea81c59ba718f6c
GitHub-Pull-Request: golang/website#6
Reviewed-on: https://go-review.googlesource.com/c/website/+/208158
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/internal/dl/dl.go b/internal/dl/dl.go
index 4aa760a..7e37f36 100644
--- a/internal/dl/dl.go
+++ b/internal/dl/dl.go
@@ -336,7 +336,7 @@
 }
 
 var (
-	fileRe  = regexp.MustCompile(`^go[0-9a-z.]+\.[0-9a-z.-]+\.(tar\.gz|pkg|msi|zip)$`)
+	fileRe  = regexp.MustCompile(`^go[0-9a-z.]+\.[0-9a-z.-]+\.(tar\.gz|tar\.gz\.asc|pkg|msi|zip)$`)
 	goGetRe = regexp.MustCompile(`^go[0-9a-z.]+\.[0-9a-z.-]+$`)
 )