Eric Glyman and Karim Atiyeh, cofounders of corporate card startup Ramp Corporate charge card start-up Ramp has more than doubled its valuation since its previous funding round just five months ago amid torrid revenue growth and strong demand for fintech investments. Ramp is raising $300 million in a Series C round at a $3.9 billion valuation, according to CEO and co-founder Eric Glyman. The New York-based firm last raised money in April at a $1.6 billion valuation. The company, which competes with legacy players including American Express and disruptors such as Brex, has struck a chord with small- and medium-sized businesses by promising to save users money and time. That’s…