Fix a bug while creating initial symlinks

src/Handler.php

@@ -107,7 +107,7 @@ class Handler extends BaseHandler {
     // Link Drupal site's files and private directory.
     foreach (['files', 'private'] as $dir) {
       if (!$fs->exists($webRoot . '/sites/default/' . $dir)) {
-        $rel = substr($fs->makePathRelative($projectRoot . '/files/default/' . $dir, $projectRoot . '/' . $webRoot . '/sites/default/' . $dir), 3, -1);
+        $rel = substr($fs->makePathRelative($projectRoot . '/files/default/' . $dir, $projectRoot . '/' . $webRoot . '/sites/default'), 3, -1);
         $fs->symlink($rel, $webRoot . '/sites/default/' . $dir);
         $fs->chmod($webRoot . '/sites/default/' . $dir, 0775);
       }