NEW YORK, Oct 14 — The United States has overtaken China as the biggest miner of bitcoin following Beijing’s crackdown on the method used to unearth the world’s major cryptocurrency, a study showed on Wednesday. Figures released by the University of Cambridge showed that activity in the US more than doubled in the four months to the end of August, increasing the market share held by the world’s biggest economy to 35.4 per cent. Kazakhstan, in second place, also more than doubled its activity to 18.1 per cent, followed by Russia with 11 per cent, said Michel Rauchs at the…