debian/control: mark package as incompatible with gtk3 >= 3.20

Addresses #13.

debian/changelog

@@ -1,3 +1,11 @@
+bunsen-themes (8.3.1-2) bunsen-hydrogen; urgency=medium
+
+  * Mark theme suite as incompatible with gtk3 >= 3.20. This will make the
+    themes unavailable on stretch and newer but ensure that users do not end
+    up with broken themes.
+
+ -- Jens John <[email protected]>  Mon, 10 May 2016 00:17:34 +0900
+
 bunsen-themes (8.3.1-1) bunsen-hydrogen; urgency=low
 
   * Non-maintainer upload.

debian/control

@@ -10,7 +10,7 @@ Vcs-Git: https://github.com/BunsenLabs/bunsen-themes.git
 
 Package: bunsen-themes
 Architecture: all
-Depends: gtk2-engines-murrine, gtk2-engines-pixbuf, libgtk-3-0, ${misc:Depends}
+Depends: gtk2-engines-murrine, gtk2-engines-pixbuf, libgtk-3-0 (<< 3.20), ${misc:Depends}
 Suggests: openbox, lightdm-gtk-greeter
 Description: GTK, Openbox, and Li themes for Bunsen and Debian Jessie
  Made by hhh from the Crunchbang forums