Import Foundation also on Linux

Sources/HttpServerIO.swift

@@ -5,10 +5,9 @@
 //  Copyright (c) 2014-2016 Damian Kołakowski. All rights reserved.
 //
 
+import Foundation
 #if os(Linux)
     import Glibc
-#else
-    import Foundation
 #endif
 
 public class HttpServerIO {