Update the 1.8.1 hotfix manifest

The ep-engine branch it points to no longer exists

Change-Id: I1d8f54d6e1a9a11030446e3c9a87be6801a79a18
Reviewed-on: http://review.couchbase.org/25347
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>