Default chunk size is using wrong unit

[1owell]

My team is running into timeout issues while uploading files from iOS. We use the defaultDirectUploadChunkSize property which sets the default chunk size to 8 MB. According to Google Cloud's upload documentation and other initializers for DirectUploadOptions.Transport this should be specified as 8 MiB (mebibytes).

In my testing this fixed our upload timeout issues.

[andrewjl-mux]

Hey @1owell!

Thanks for reporting your test results and including the Google Cloud documentation. We'll improve this.