Update Async Kit to latest version. (#329)

Update Async Kit to latest version.

Author: Freelenzer

Package.swift

@@ -15,7 +15,7 @@ let package = Package(
     dependencies: [
         .package(url: "https://github.com/vapor/mysql-nio.git", from: "1.7.2"),
         .package(url: "https://github.com/vapor/sql-kit.git", from: "3.29.3"),
-        .package(url: "https://github.com/vapor/async-kit.git", from: "1.19.0"),
+        .package(url: "https://github.com/vapor/async-kit.git", from: "1.20.0"),
         .package(url: "https://github.com/apple/swift-crypto.git", "2.0.0" ..< "4.0.0"),
         .package(url: "https://github.com/apple/swift-nio.git", from: "2.65.0"),
         .package(url: "https://github.com/apple/swift-nio-ssl.git", from: "2.26.0"),