[gimp] Mention newly added pass-through layer group mode in NEWS

[Alexandre Prokoudine <aprokoudine src gnome org>]

commit 4e17291e5290fd34947d9c0fe09f1c41ffe6e763
Author: Alexandre Prokoudine <alexandre prokoudine gmail com>
Date:   Tue Aug 8 23:11:00 2017 +0300

    Mention newly added pass-through layer group mode in NEWS

 NEWS |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/NEWS b/NEWS
index e6bf185..6e66e0b 100644
--- a/NEWS
+++ b/NEWS
@@ -47,7 +47,8 @@ Layers and compositing:
   - Layer blending color space and compositing color space are
     configurable now.
   - New layer modes: linear burn, vivid light, linear light, pin light,
-    hard mix, exclusion, merge, split, luminance (rgb).
+    hard mix, exclusion, merge, split, luminance (rgb), pass-through
+    (for layer groups only).
   - Make erase mode an ordinary layer/paint mode.
   - Better performance of HSV-based layer modes.
   - Rename "Color (HSV)" mode to "Color (HSL)" to indicate the actual
@@ -204,7 +205,8 @@ File Formats:
   - Handle linear gamma PNG files correctly, provide a combo box for
     specifying PNG bit depth / variant at exporting time.
   - Add support for linear burn, linear light, vivid light, pin light,
-    and hard mix layer modes in PSD (importing and exporting).
+    hard mix, and pass-through layer modes in PSD (importing and
+    exporting).
   - Load PSD files with layers which contain additional information
     with a length that is not divisible by 4.
   - Add support to import/export layer color tags from/to PSD files.