Anheuser-Busch InBev is having a tough time getting millennials to crack open a can of Budweiser. The world’s biggest brewer said Thursday that falling unemployment and “premium” brands are boosting overall beer sales in the US, its biggest market. But the company is struggling to market Bud — the 139-year-old American brand with blue-collar roots — to younger drinkers, who prefer craft brews and bourbon.