MB-100: fix ep_engine repo in toy build manifest

Change-Id: I91b6bf355dff102ed399d22feac29efc6b12df0a
Reviewed-on: http://review.couchbase.org/28563
Reviewed-by: Junyi Xie <junyi.couchbase@gmail.com>
Tested-by: Junyi Xie <junyi.couchbase@gmail.com>