[gtk-doc] Also bump version in meson.build

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 29890a25995c7b81bb4f11d1ed05f9b9463379f1
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Tue Aug 6 11:05:59 2019 -0500

    Also bump version in meson.build

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 85e83ca..5e4d288 100644
--- a/meson.build
+++ b/meson.build
@@ -1,5 +1,5 @@
 project('gtk-doc', 'c',
-  version: '1.30.1',
+  version: '1.31',
   license: 'GPL2+',
   meson_version: '>= 0.50.0', # needed for https://mesonbuild.com/Python-module.html#path
 )