add 'time()' method to MultiKeyPipellineBase

Dear Professor xetorthio,

First thank u for creating the jedis, and recently my company use jedis pipeline and we want to get the time when redis execute the commands which pipeline send to. so we add time() method in the class 'MultiKeyPipellineBase' and we hope u checking and merging it :)  thanks again !

Sincerely yours,
PumpkinJack