scripts/sha512sum.sh: output error message to stderr

scripts/sha512sum.sh

@@ -11,7 +11,7 @@ elif check_command shasum; then
 elif check_command cksum; then
 	ret="$(cksum -q -a sha512 "$@")"
 else
-	echo "$0: no suitable sha512sum implementation was found" >&1
+	echo "$0: no suitable sha512sum implementation was found" >&2
 	exit 1
 fi