Specify bash

If the test vectors do not pass the script fails when using sh

Change-Id: I2f577c46328ff6d9c884ff483f742bf8d5f76686
diff --git a/run_tests.sh b/run_tests.sh
index 7858c0a..7a8fe1d 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 self=$0
 self_basename=${self##*/}
 EOL=$'\n'