[gnome-builder] build: bump c++ requirement

[Christian Hergert <chergert src gnome org>]

commit 4295d7d89fd6a7c45194cb05e1356bf4daefb399
Author: Christian Hergert <chergert redhat com>
Date:   Tue Apr 2 12:05:09 2019 -0700

    build: bump c++ requirement
    
    We are currently using __VA_OPT__ (which we can certainly remove, but it's
    there for now so we should be clear about it).

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 6cbf6fed8..dd6b1e0e1 100644
--- a/meson.build
+++ b/meson.build
@@ -3,7 +3,7 @@ project('gnome-builder', 'c',
           version: '3.33.0',
     meson_version: '>= 0.50.0',
   default_options: [ 'c_std=gnu11',
-                     'cpp_std=c++11',
+                     'cpp_std=gnu++2a',
                      'warning_level=2',
                      'channel=other',
                    ],