Raise minimum Swift version to 5.8 (#729)

Author: glbrntt

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.7
+// swift-tools-version:5.8
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the AsyncHTTPClient open source project

README.md

@@ -329,4 +329,5 @@ AsyncHTTPClient     | Minimum Swift Version
 `1.10.0 ..< 1.13.0` | 5.4
 `1.13.0 ..< 1.18.0` | 5.5.2
 `1.18.0 ..< 1.20.0` | 5.6
-`1.20.0 ...`        | 5.7
+`1.20.0 ..< 1.21.0` | 5.7
+`1.21.0 ...`        | 5.8

docker/docker-compose.2204.510.yaml

@@ -6,7 +6,8 @@ services:
     image: async-http-client:22.04-5.10
     build:
       args:
-        base_image: "swiftlang/swift:nightly-5.10-jammy"
+        ubuntu_version: "jammy"
+        swift_version: "5.10"
 
   documentation-check:
     image: async-http-client:22.04-5.10