[Sprint 38] XD-2323 Fix Batch replyChannel Header

JIRA: https://jira.spring.io/browse/XD-2323

Spring Integration 4.1.0 incorrectly mapped the `replyChannel`
header as a String, preventing the replacement with
the `xdReplyChannel` (transmitted as a String to the slave).

See INT-3555.

Set `overwrite="true"`.