Add missing `use` in HgDriver

Closes #1165

src/Composer/Repository/Vcs/HgDriver.php

@@ -14,6 +14,7 @@ namespace Composer\Repository\Vcs;
 
 use Composer\Json\JsonFile;
 use Composer\Util\ProcessExecutor;
+use Composer\Util\Filesystem;
 use Composer\IO\IOInterface;
 
 /**