fix os.copy

Author: pawelsadlo

os/src/FileOps.scala

@@ -202,7 +202,7 @@ object copy {
 
     def copyOne(p: Path): Unit = {
       val target = to / p.relativeTo(from)
-      if (mergeFolders && isDir(p, followLinks) && isDir(target, followLinks)) {
+      if (mergeFolders && isDir(p, followLinks) && (isDir(target, followLinks) ||  !exists(target,followLinks))) {
         // nothing to do
       } else {
         Files.copy(p.wrapped, target.wrapped, opts1 ++ opts2 ++ opts3: _*)