Filename isn't respected for string attachments

[cprussin]

If I pass an attachment where the data is a string, the filename & contentType are ignored. For instance:

mg.messages.create("somedomain.com", {
    ...,
    attachment: {
        filename: 'my-cool-attachment.csv',
        data: 'check,this,stuff,out',
        contentType: 'text/csv'
    }
});

The issue appears to be caused by these lines which do not use the filename in any way.

I'm happy to put in a fix but I don't know enough about the form data stuff going on in this library and I know there's a lot of backward compatibility so I'd need some guidance on what the right fix is... I'm guessing we should wrap the string body in a Blob before passing to FormData so that we can append the filename.

There's probably some other stuff affected here too....

[chidg]

Ran into this issue. Wrapping the string in Buffer.from solved it.