The resurgence of volatility that dominated the U.S. stock market in early 2018 has already vanished. And some investors are betting tranquility will continue in equities. Investors including hedge funds have increased wagers that futures contracts tracking the Cboe Volatility Index will fall. The gauge, dubbed the VIX, measures expectations for equity price swings over the next month. After much turbulence, the S&P 500 has crept higher and is now up 3.7% this year. Technology companies have powered the benchmark equity gauge higher.