Open links in new window/tab

Hi Nick, great plugin! We have run into one roadblock though…

We are linking our images to external pages but we would like to have those links open into a new tab/window. I haven’t been able to get this to work. Is it possible? If so, how? I tried using target=_blank in the image link field but it didn’t work.

https://wordpress.org/plugins/space-boxes/