Use prefixed temp folder

Summary:
I'm accumulating a lot of those in my tmpfs and
it would be great to immediately identify the
ones coming from Flipper.

Reviewed By: danielbuechele

Differential Revision: D14406809

fbshipit-source-id: 6b74e8260a841d5db76ac34643ee0226abba735a

scripts/build-utils.js

@@ -79,7 +79,7 @@ function buildFolder() {
   // eslint-disable-next-line no-console
   console.log('Creating build directory');
   return new Promise((resolve, reject) => {
-    tmp.dir((err, buildFolder) => {
+    tmp.dir({prefix: 'flipper-build-'}, (err, buildFolder) => {
       if (err) {
         reject(err);
       } else {