Avoids trying to stringify a huge array

When using `JSON.stringify` on a large array (200k items), it may
run out of memory and give an error. We run into this error at the
end of generation when we write to `build/json/_metadata.json`.

This commit makes it only stringify one item at a time, which is
probably slower, but avoids the error (could probably add logic to
only do this if needed).

src/main.js

@@ -549,7 +549,7 @@ const startCreating = () => {
 
     return true;
   });
-  writeMetaData(JSON.stringify(metadataList, null, 2));
+  writeMetaData(`[${metadataList.map(e => JSON.stringify(e, null, 2)).join(',')}]`);
 };
 
 module.exports = { startCreating, buildSetup, getElements };