Pre-release bump version to 0.12.0

This version bump makes it clear that this is not a 0.11.x
version, as the removal of setuid support is a major behaviour
change.

Author: alexlarsson

meson.build

@@ -1,7 +1,7 @@
 project(
   'bubblewrap',
   'c',
-  version : '0.11.2',
+  version : '0.12.0',
   meson_version : '>=0.49.0',
   default_options : [
     'warning_level=2',