Have xcopy overwrite existing files

src/Composer/Util/Filesystem.php

@@ -266,7 +266,7 @@ class Filesystem
 
         if (defined('PHP_WINDOWS_VERSION_BUILD')) {
             // Try to copy & delete - this is a workaround for random "Access denied" errors.
-            $command = sprintf('xcopy %s %s /E /I /Q', ProcessExecutor::escape($source), ProcessExecutor::escape($target));
+            $command = sprintf('xcopy %s %s /E /I /Q /Y', ProcessExecutor::escape($source), ProcessExecutor::escape($target));
             $result = $this->processExecutor->execute($command, $output);
 
             // clear stat cache because external processes aren't tracked by the php stat cache