[gimp] libgimpwidgets: install gimpspinbutton.h

[Ell <ell src gnome org>]

commit 03a928409a46c1255dae6e238cc0d89a07fe76bb
Author: Ell <ell_se yahoo com>
Date:   Mon Nov 19 09:27:01 2018 -0500

    libgimpwidgets: install gimpspinbutton.h
    
    Added in commit 7ab9ee268637093902ec243a30d6a96437eba3fc.

 libgimpwidgets/Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/libgimpwidgets/Makefile.am b/libgimpwidgets/Makefile.am
index 51c3a618b8..2e3ee30e99 100644
--- a/libgimpwidgets/Makefile.am
+++ b/libgimpwidgets/Makefile.am
@@ -262,6 +262,7 @@ libgimpwidgetsinclude_HEADERS = \
        gimpscaleentry.h                \
        gimpscrolledpreview.h           \
        gimpsizeentry.h                 \
+       gimpspinbutton.h                \
        gimpstringcombobox.h            \
        gimpunitcombobox.h              \
        gimpunitstore.h                 \