[sysprof] build: bump to gtk+ 3.21.6 for natural scrolling fixes

[Christian Hergert <chergert src gnome org>]

commit 1f3982bd87fd85611c7278aa2af1e2249d3a5c2d
Author: Christian Hergert <chergert redhat com>
Date:   Tue Sep 13 11:10:26 2016 -0700

    build: bump to gtk+ 3.21.6 for natural scrolling fixes

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index cb96c7a..5b580ed 100644
--- a/configure.ac
+++ b/configure.ac
@@ -112,7 +112,7 @@ dnl ***********************************************************************
 dnl Check for required packages
 dnl ***********************************************************************
 m4_define([glib_required_version], [2.44.0])
-m4_define([gtk_required_version], [3.21.5])
+m4_define([gtk_required_version], [3.21.6])
 m4_define([systemd_required_version], [222])
 
 PKG_CHECK_MODULES(GIO,