Ensure distDir exists

Summary:
That avoids failures like these:

{F693123233}

Reviewed By: aigoncharov

Differential Revision: D33585422

fbshipit-source-id: b2b5af2daf7beaa796b331c5988e51ea3ed94699

desktop/scripts/build-flipper-server-release.ts

@@ -245,6 +245,7 @@ async function modifyPackageManifest(
 
 async function packNpmArchive(dir: string, versionNumber: any) {
   console.log(`⚙️  Packing flipper-server.tgz`);
+  await fs.mkdirp(distDir);
   const archive = path.resolve(distDir, 'flipper-server.tgz');
   await spawn('yarn', ['pack', '--filename', archive], {
     cwd: dir,