Bug#972791: setzer: "Namespace GtkSource not available for version 4"

[Nable]

Hi,

I came across the same problem. I've solved it locally by installing 
"gir1.2-gtksource-4" and "gir1.2-webkit2-4.0" packages in addition to "setzer" 
(missing package names are obvious after reading stack traces). It looks like 
the current .deb package (0.3.1-2) has an incomplete value for "Depends" field. 
I hope it'll be fixed soon.