A Seattle-based app that lets shops and restaurants pay for their customers' Lyft and Uber rides is expanding into eight more cities. Launched last year to serve Seattle and Portland, Validated is now available in Boston, Chicago, Washington, D.C., Las Vegas, Los Angeles, New York City and four cities in California: Palo Alto, San Diego, San Francisco and Santa Monica. The free mobile app lets retailers pay for a customer's transportation as a way to show appreciation, drive sales and keep them…