* Holdings of SPDR Gold Trust GLD, the world's largest gold-backed exchange-traded fund, fell 6.08 tonnes on Wednesday, their biggest one-day outflow since July. Oct 20 (Reuters) - Gold prices lingered at a three-week trough on Thursday, pressured by rising U.S. dollar and Treasury yields amid worries that the Federal Reserve will persist with sharp rate hikes. * With latest data showing inflation continuing to run at more than three times the central bank's 2% target, the report may do little to temper expectations for a fourth straight 75-basis-point rate hike next month.