Wait for the modules directory to be created before writing module files

Summary: Typo: the operation of writing module files to a common sub-directory didn?t wait until that directory was created, because `Promise.all` was invoked directly as argument to `.then()`, rather than putting it in a lambda function.

Reviewed By: andreicoman11

Differential Revision: D3150338

fb-gh-sync-id: c65270b1757a248993048b039f5ebadb281b2eea
fbshipit-source-id: c65270b1757a248993048b039f5ebadb281b2eea

local-cli/bundle/output/unbundle/as-assets.js

@@ -41,7 +41,7 @@ function saveAsAssets(bundle, options, log) {
   const modulesDir = path.join(path.dirname(bundleOutput), MODULES_DIR);
   const writeUnbundle =
     createDir(modulesDir).then( // create the modules directory first
-      Promise.all([
+      () => Promise.all([
         writeModules(modules, modulesDir, encoding),
         writeFile(bundleOutput, startupCode, encoding),
         writeMagicFlagFile(modulesDir),