[gnome-calendar] project: bump gtk+ min version

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 4e7706847e56858f91b5cb2627467b1cfd120943
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Sep 14 14:16:37 2016 -0300

    project: bump gtk+ min version
    
    We use features of the latest release 3.21.6, so make it a
    requirement.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 7bca982..ed7c1d6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -76,7 +76,7 @@ AC_PATH_PROG([GLIB_MKENUMS], [glib-mkenums])
 AX_COMPILER_FLAGS
 
 GLIB_MIN_VERSION=2.43.4
-GTK_MIN_VERSION=3.21.1
+GTK_MIN_VERSION=3.21.6
 ECAL_REQUIRED=3.13.90
 EDATASERVER_REQUIRED=3.17.1
 EDATASERVERUI_REQUIRED=3.17.1