Use /bin/bash for release-util sign.sh script
diff --git a/release-utils/scripts/sign.sh b/release-utils/scripts/sign.sh
index ae22f18..e0d7b05 100755
--- a/release-utils/scripts/sign.sh
+++ b/release-utils/scripts/sign.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 # Licensed to the Apache Software Foundation (ASF) under one or more
 # contributor license agreements.  See the NOTICE file distributed with