[gimp] plug-ins: one more missing backslash.

[Jehan <jehanp src gnome org>]

commit c63ae2f94509aa91629d7e9839df20380a7b9628
Author: Jehan <jehan girinstud io>
Date:   Mon Jul 29 00:15:56 2019 +0200

    plug-ins: one more missing backslash.
    
    Come on!

 plug-ins/lighting/images/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/plug-ins/lighting/images/Makefile.am b/plug-ins/lighting/images/Makefile.am
index 9fa1d65e10..ecfda93401 100644
--- a/plug-ins/lighting/images/Makefile.am
+++ b/plug-ins/lighting/images/Makefile.am
@@ -12,7 +12,7 @@ STOCK_IMAGES = \
        lighting-reflectivity-highlight-high.png        \
        lighting-reflectivity-highlight-low.png
 
-EXTRA_DIST =
+EXTRA_DIST = \
        $(STOCK_IMAGES)         \
        lighting-icon-images.gresource.xml