[geary] build: Bump minimum GLib version to 2.64

[Michael Gratton <mjog src gnome org>]

commit d6ed4768bfc7896f84c58d453e35d4e002b12e91
Author: Michael Gratton <mike vee net>
Date:   Sun Aug 23 17:40:28 2020 +1000

    build: Bump minimum GLib version to 2.64
    
    This should have been included in !554, but wasn't.

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index d649a6e17..30191e750 100644
--- a/meson.build
+++ b/meson.build
@@ -51,7 +51,7 @@ valac = meson.get_compiler('vala')
 #
 
 target_vala = '0.48.6'
-target_glib = '2.60.4'
+target_glib = '2.64'
 target_gtk = '3.24.7'
 target_webkit = '2.26'