fix(composer): ensure vendor dir exists

lib/manager/composer/artifacts.js

@@ -27,6 +27,7 @@ async function getArtifacts(
     return null;
   }
   const cwd = upath.join(config.localDir, upath.dirname(packageFileName));
+  await fs.ensureDir(upath.join(cwd, 'vendor'));
   let stdout;
   let stderr;
   try {