godoc: use ARMv6 as the label for arm6 builds.

Change-Id: I53c51fb772f23ab3f035b8e50bf017335d01e1c4
Reviewed-on: https://go-review.googlesource.com/18019
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

godoc/dl/dl.go

@@ -434,6 +434,8 @@ var prettyStrings = map[string]string{
 	"386":   "32-bit",
 	"amd64": "64-bit",
 
+	"arm6": "ARMv6",
+
 	"archive":   "Archive",
 	"installer": "Installer",
 	"source":    "Source",