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) && !exists(target,followLinks)) {
+      if (mergeFolders && isDir(p, followLinks) && !isLink(p) && !exists(target, followLinks)) {
         os.makeDir(target)
       } else if (mergeFolders && isDir(p, followLinks) && isDir(target, followLinks)) {
         // nothing to do