SINGAPORE – China’s giant coffee chain Luckin Coffee makes its debut in Singapore with a double shot: Two stores – at Marina Square and Ngee Ann City – opened on Friday, with more in the works. Singapore is the first market in its overseas expansion. Nicknamed the Starbucks of China, the brand has more than 8,000 stores in its home country. Luckin Coffee sets itself as a disruptor with its use of big data and full mobile ordering and cashless payment system via its mobile app, says the brand’s spokesman. This eliminates the need to queue if orders are placed...