PayPal-owned Venmo is expanding its support for cryptocurrency with today’s launch of a new feature that will allow users to automatically buy cryptocurrency using the cash back they earned from their Venmo credit card purchases. Unlike when buying cryptocurrency directly, these automated purchases will have no transaction fees associated with them — a feature Venmo says is not a promotion, but how the system will work long term. Instead, a cryptocurrency conversion spread is built into each monthly transaction. Cardholders will be able to purchase Bitcoin, Ethereum, Litecoin and Bitcoin…