Vapor 3 RC 2 is out! To update, ensure that your Package.swift contains something like:
.package(url: "https://github.com/vapor/vapor.git", from: "3.0.0-rc"),
.package(url: "https://github.com/vapor/fluent-mysql.git", from: "3.0.0-rc"),
.package(url: "https://github.com/vapor/leaf.git", from: "3.0.0-rc"),