By Kylie MacLellan and Alistair Smout LONDON (Reuters) -Britain’s former finance minister Rishi Sunak held onto his lead in the race to become Britain’s next prime minister on Monday as another hopeful was knocked out, leaving four candidates in an increasingly bitter contest to replace Boris Johnson. Sunak got 115 votes in the third ballot of Conservative lawmakers on Monday, ahead of former defence minister Penny Mordaunt on 82 and Foreign Secretary Liz Truss on 71. Since Johnson said he would resign earlier this month after his scandal-ridden administration lost the support of many in his r…