Make /bin/bash explicit in make_pkginfo

/bin/sh is not always /bin/bash, and double bracket evaluations don't work on all sh implementations.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134998874

java/google/registry/xjc/make_pkginfo.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 # Copyright 2016 The Domain Registry Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");