using mkdir() in copyThenRemove() leads to errors if the target exists or not a dir, use ensureDirectoryExists() instead

src/Composer/Util/Filesystem.php

@@ -129,15 +129,12 @@ class Filesystem
     {
         $it = new RecursiveDirectoryIterator($source, RecursiveDirectoryIterator::SKIP_DOTS);
         $ri = new RecursiveIteratorIterator($it, RecursiveIteratorIterator::SELF_FIRST);
-
-        if (!file_exists($target)) {
-            mkdir($target, 0777, true);
-        }
+        $this->ensureDirectoryExists($target);
 
         foreach ($ri as $file) {
             $targetPath = $target . DIRECTORY_SEPARATOR . $ri->getSubPathName();
             if ($file->isDir()) {
-                mkdir($targetPath);
+                $this->ensureDirectoryExists($targetPath);
             } else {
                 copy($file->getPathname(), $targetPath);
             }