[babl] tests/grayscale_to_rgb: increase printed debug precision

[Øyvind Kolås <ok src gnome org>]

commit 53c61827a8dcd2c692ddc83626bb52ea24904c74
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Sep 25 21:41:36 2017 +0200

    tests/grayscale_to_rgb: increase printed debug precision

 tests/grayscale_to_rgb.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/tests/grayscale_to_rgb.c b/tests/grayscale_to_rgb.c
index b239e23..b59da38 100644
--- a/tests/grayscale_to_rgb.c
+++ b/tests/grayscale_to_rgb.c
@@ -61,7 +61,7 @@ test (void)
     {
       if (fabs (rgb_buf[i] - rgb_buf_ref[i]) > 0.0000001)
         {
-          babl_log ("index %i is problematic : %f instead of %f",
+          babl_log ("index %i is problematic : %.12f instead of %.12f",
                     i, rgb_buf[i], rgb_buf_ref[i]);
           OK = 0;
         }