[gegl] configure: raise ffmpeg requirement to 56.0.0

[Øyvind Kolås <ok src gnome org>]

commit 4b55385c584fd511636e522ccfc722b03c6ab64c
Author: Øyvind Kolås <pippin gimp org>
Date:   Sat Nov 21 20:54:22 2015 +0100

    configure: raise ffmpeg requirement to 56.0.0
    
    This might be higher than stricly neccesary; but would avoid unnecesarily
    broken builds.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 023b18c..a9c9397 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1014,7 +1014,7 @@ AC_SUBST(LUA_LIBS)
 AC_ARG_WITH(libavformat,  [  --without-libavformat   build without libavformat support])
 
 if test "x$with_libavformat" != xno; then
-  PKG_CHECK_MODULES(AVFORMAT, libavformat >= 53.0.0 libavcodec >= 53.0.0 libswscale >= 3.1.0,
+  PKG_CHECK_MODULES(AVFORMAT, libavformat >= 56.0.0 libavcodec >= 56.0.0 libswscale >= 3.1.0,
     have_libavformat="yes",
     have_libavformat="no  (libavformat not found)")
   # verify the presence of the avformat.h header