[release-branch.go1.10] godoc/dl: add valsorda to users allowed to upload

Change-Id: Iac4a80b030be9c275323a27d2dfba4f83942cbf9
Reviewed-on: https://go-review.googlesource.com/117195
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 4e38c85762)
Reviewed-on: https://go-review.googlesource.com/117215
Reviewed-by: Filippo Valsorda <filippo@golang.org>

godoc/dl/dl.go

@@ -441,7 +441,7 @@ func getHandler(w http.ResponseWriter, r *http.Request) {
 
 func validUser(user string) bool {
 	switch user {
-	case "adg", "bradfitz", "cbro", "andybons":
+	case "adg", "bradfitz", "cbro", "andybons", "valsorda":
 		return true
 	}
 	return false