[gimp] configure: libwebp dependency bumped to 0.6.0.

[Jehan Pagès <jehanp src gnome org>]

commit da4f137ac9d54c30ec48852d461f09e9d9a08199
Author: Jehan <jehan girinstud io>
Date:   Sun Jul 23 16:20:40 2017 +0200

    configure: libwebp dependency bumped to 0.6.0.
    
    This is to make use of the better logics of kmax (now that it finally
    makes sense). Adding now, since it is now available in Debian Testing.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 84de0aa..dab4953 100644
--- a/configure.ac
+++ b/configure.ac
@@ -76,7 +76,7 @@ m4_define([openexr_required_version], [1.6.1])
 m4_define([gtk_mac_integration_required_version], [2.0.0])
 m4_define([intltool_required_version], [0.40.1])
 m4_define([python2_required_version], [2.5.0])
-m4_define([webp_required_version], [0.5.1])
+m4_define([webp_required_version], [0.6.0])
 m4_define([webpmux_required_version], [0.5.1])
 m4_define([webpdemux_required_version], [0.5.1])