We are aware of this issue and that it has come about with the latest Chrome update. In order to download the WpStream Theme, you can right click on the link and open in new tab/window. The download zip should work at this point.
Furthermore, you can also try downloading it on a different browser as this issue is specific to Chrome and should work just fine on any other browser.
Sorry for the inconvenience and please let us know if you require anything else.