Fix access level for init and other tweaks

Fixes #6

Sources/Defaults/Defaults.swift

@@ -1,14 +1,16 @@
 // MIT License © Sindre Sorhus
-import Cocoa
+import Foundation
 
 public final class Defaults {
-	public class Keys {}
+	public class Keys {
+		fileprivate init() {}
+	}
 
 	public final class Key<T: Codable>: Keys {
 		fileprivate let name: String
 		fileprivate let defaultValue: T
 
-		init(_ key: String, default defaultValue: T) {
+		public init(_ key: String, default defaultValue: T) {
 			self.name = key
 			self.defaultValue = defaultValue
 		}
@@ -17,7 +19,7 @@ public final class Defaults {
 	public final class OptionalKey<T: Codable>: Keys {
 		fileprivate let name: String
 
-		init(_ key: String) {
+		public init(_ key: String) {
 			self.name = key
 		}
 	}

Tests/DefaultsTests/DefaultsTests.swift

@@ -1,5 +1,5 @@
 import XCTest
-@testable import Defaults
+import Defaults
 
 let fixtureUrl = URL(string: "httos://sindresorhus.com")!