[gegl] tests: update contrast curve reference

[Øyvind "pippin" Kolås <ok src gnome org>]

commit ff8278f674763b9d31ed0dcba7321cdd46296d0c
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Jul 2 09:27:40 2018 +0200

    tests: update contrast curve reference

 tests/compositions/reference/contrast-curve.png | Bin 265342 -> 265335 bytes
 1 file changed, 0 insertions(+), 0 deletions(-)
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diff --git a/tests/compositions/reference/contrast-curve.png b/tests/compositions/reference/contrast-curve.png
index 267a7859d..c23a6bc7d 100644
Binary files a/tests/compositions/reference/contrast-curve.png and 
b/tests/compositions/reference/contrast-curve.png differ