[gnome-documents] build: Update minimum meson version

[Christopher Davis <christopherdavis src gnome org>]

commit 1c140317f02eb48cc099ec3547a58be91bad7025
Author: Christopher Davis <brainblasted disroot org>
Date:   Mon Aug 5 20:41:03 2019 -0700

    build: Update minimum meson version
    
    We use features from 0.50.0.

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 7a6e7429..97df37e7 100644
--- a/meson.build
+++ b/meson.build
@@ -3,7 +3,7 @@ project(
   version: '3.32.0',
   license: 'GPL2+',
   default_options: 'buildtype=debugoptimized',
-  meson_version: '>= 0.42.0'
+  meson_version: '>= 0.50.0'
 )
 
 documents_version = meson.project_version()