MB-100: fix ep-engine branch in toy-junyi manifest file

Change-Id: I2a1f00a58db9fea4cab6f886f3f955b5ffb2c669
Reviewed-on: http://review.couchbase.org/27962
Reviewed-by: Junyi Xie <junyi.couchbase@gmail.com>
Tested-by: Junyi Xie <junyi.couchbase@gmail.com>