In the salad days of bitcoin, venture capital firms bought into the craze in a roundabout way. Instead of simply purchasing bitcoins, they invested in companies like Coinbase, which makes a wallet for digital currencies, or 21.co, which aimed to improve the process of mining coins. Some of these bets were better than others. 21 has changed names and business plans, but Coinbase’s app hit the No. 1 spot on Apple’s App Store this month as the hyperventilation over bitcoin reached an extreme.