Backport to Swift 5.1

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.2
+// swift-tools-version:5.1
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription

Sources/Conf/Key.swift

@@ -8,7 +8,7 @@ public struct Key {
     }
 
     public init(_ elements: [LosslessStringConvertible]) {
-        path = elements.map(\.description)
+        path = elements.map { $0.description }
     }
 
     public init(_ elements: LosslessStringConvertible...) {

Tests/ConfTests/ConfigTests.swift

@@ -69,7 +69,7 @@ final class ConfigTests: XCTestCase {
             }
         }
 
-        XCTAssertThrowsError(try config.require("missingLossless") as Int?) { error in
+        XCTAssertThrowsError(try config.require("missingLossless") as Int) { error in
             if case let ConfigurationError.missing(key: key) = error {
                 XCTAssertEqual(key, "missingLossless")
             } else {