Linux: Add dependency to NSLinux

Package.swift

@@ -1,5 +1,8 @@
 import PackageDescription
 
 let package = Package(
-    name: "Swifter"
+    name: "Swifter",
+    dependencies: [
+        .Package(url: "https://github.com/johnno1962/NSLinux.git", majorVersion: 1),
+    ]
 )

Sources/Swifter/HttpServer.swift

@@ -6,6 +6,10 @@
 
 import Foundation
 
+#if os(Linux)
+    import NSLinux
+#endif
+
 public class HttpServer {
     
     static let VERSION = "1.0.2";