Increase minimum required version of Swift-Nio to 2.78.0 (#159)

Recent changes make use of some methods that weren't introduced to Swift-Nio until 2.78.0.

Author: robinkunde

Package.swift

@@ -13,7 +13,7 @@ let package = Package(
         .library(name: "WebSocketKit", targets: ["WebSocketKit"]),
     ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-nio.git", from: "2.53.0"),
+        .package(url: "https://github.com/apple/swift-nio.git", from: "2.78.0"),
         .package(url: "https://github.com/apple/swift-nio-extras.git", from: "1.16.0"),
         .package(url: "https://github.com/apple/swift-nio-ssl.git", from: "2.24.0"),
         .package(url: "https://github.com/apple/swift-nio-transport-services.git", from: "1.16.0"),