By Gerry Shih SAN FRANCISCO (Reuters) – Stripe Inc has joined the billion-dollar club. The online payment-processing startup announced Wednesday it raised $80 million from venture capital investors in a deal that values Stripe at a hefty $1.75 billion. The transaction places the 90-person firm in the rarefied company of startups valued at more than $1 billion just three years after brothers Patrick and John Collison, now ages 25 and 23, debuted their service. Chief Executive Patrick Collison said the lofty valuation reflected the promise shown by his company, which processed billions of dollars in payments last year for businesses ranging from Lyft, the ridesharing company, to the Museum of Modern Art in New York.