[firebase-storage] customMetadata cannot be set on IOS

[canmertc]

I'm using the following code to upload files with metadata to the default bucket. It works on Android as expected but customMetadata property cannot be set on IOS.

// File upload with custom metadata
const metadata = new Metadata();
metadata.customMetadata = {
  foo: "bar"
};

const defaultBucket = firebase().storage();
const reference = defaultBucket.ref(remotePath);
const task = reference.putFile(localPath, metadata);