[gnome-screenshot] build: post-release version bump to 3.31.0

[Cosimo Cecchi <cosimoc src gnome org>]

commit 6fe29e1d8ede0b8f316726b6b9adeb1c32da285a
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Mon Sep 3 16:35:17 2018 -0700

    build: post-release version bump to 3.31.0

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index b42c345..08c77b1 100644
--- a/meson.build
+++ b/meson.build
@@ -1,5 +1,5 @@
 project('gnome-screenshot', 'c',
-        version: '3.30.0',
+        version: '3.31.0',
         license: 'GPLv2+',
         meson_version: '>= 0.40.1',
         default_options: [