U.S.-based challenger bank Current, which has now grown to nearly 3 million users, announced this morning it has raised a $220 million round of Series D funding, led by new investor Andreessen Horowitz (a16z). The funding swiftly follows Current’s $131 million Series C at the end of last year, at which point the company had doubled its user base over just six months to over 2 million users. As a result of the new roud, the fintech company has roughly tripled its valuation in five months’ time to $2.2 billion….