[gimp] plug-ins: link goat-exercise against GTK

[Michael Natterer <mitch src gnome org>]

commit 7f0c801559955fa1c0f8082596e86dc83d735a1e
Author: Michael Natterer <mitch gimp org>
Date:   Wed Aug 7 18:43:04 2019 +0200

    plug-ins: link goat-exercise against GTK

 plug-ins/goat-exercises/Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/plug-ins/goat-exercises/Makefile.am b/plug-ins/goat-exercises/Makefile.am
index 14ce1f3b01..3a7394d885 100644
--- a/plug-ins/goat-exercises/Makefile.am
+++ b/plug-ins/goat-exercises/Makefile.am
@@ -52,6 +52,7 @@ goat_exercise_LDADD = \
        $(CAIRO_LIBS)           \
        $(GDK_PIXBUF_LIBS)      \
        $(GEGL_LIBS)            \
+       $(GTK_LIBS)             \
        $(RT_LIBS)              \
        $(INTLLIBS)             \
        $(goat_exercise_RC)