[geary] Fix target GLib version in Meson build.

[Michael Gratton <mjog src gnome org>]

commit 147dd8e4c0fb027b62b78b79994cea683ba1be09
Author: Michael James Gratton <mike vee net>
Date:   Mon Dec 18 10:31:02 2017 +1100

    Fix target GLib version in Meson build.

 meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/meson.build b/meson.build
index 99c02af..49b7aaa 100644
--- a/meson.build
+++ b/meson.build
@@ -36,7 +36,7 @@ add_project_arguments([
 )
 
 # Dependencies
-target_glib = '2.44' # Also passed to valac, so don't include a point rev
+target_glib = '2.50' # Also passed to valac, so don't include a point rev
 target_gtk = '3.22.0'
 target_webkit = '2.16'