Invalidate file cache upon copying folders

Author: janschoenherr

src/Folder.php

@@ -88,6 +88,7 @@ public static function copy($src, $dest, $path = '', $force = false, $useStreams
                         if (!@copy($sfid, $dfid)) {
                             throw new FilesystemException('Copy file failed', -1);
                         }
+                        File::invalidateFileCache($dfid);
                     }
 
                     break;