Add Swift 4 support

Package.swift

@@ -1,5 +1,5 @@
 /**
-* Copyright IBM Corporation 2016
+* Copyright IBM Corporation 2016, 2017
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
@@ -18,4 +18,4 @@ import PackageDescription
 
 let package = Package(
     name: "CHiredis",
-    dependencies: [ ])
+    dependencies: [])

Package@swift-4.swift

@@ -0,0 +1,41 @@
+// swift-tools-version:4.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+/**
+ * Copyright IBM Corporation 2016, 2017
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+import PackageDescription
+
+let package = Package(
+    name: "CHiredis",
+    products: [
+        // Products define the executables and libraries produced by a package, and make them visible to other packages.
+        .library(
+            name: "CHiredis",
+            targets: ["CHiredis"]),
+        ],
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        // .package(url: /* package url */, from: "1.0.0"),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target defines a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
+        .target(
+            name: "CHiredis",
+            dependencies: []),
+        ]
+)