[gtk+] spinbutton: Add undershoot nodes to CSS docs

[Timm Bäder <baedert src gnome org>]

commit a919f0c7f3a75226be4e3eaf633409154c166160
Author: Timm Bäder <mail baedert org>
Date:   Mon Apr 24 16:22:32 2017 +0200

    spinbutton: Add undershoot nodes to CSS docs

 gtk/gtkspinbutton.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkspinbutton.c b/gtk/gtkspinbutton.c
index 9861b14..64d3d09 100644
--- a/gtk/gtkspinbutton.c
+++ b/gtk/gtkspinbutton.c
@@ -90,6 +90,8 @@
  *
  * |[<!-- language="plain" -->
  * spinbutton.horizontal
+ * ├── undershoot.left
+ * ├── undershoot.right
  * ├── entry
  * │   ╰── ...
  * ├── button.down
@@ -98,6 +100,8 @@
  *
  * |[<!-- language="plain" -->
  * spinbutton.vertical
+ * ├── undershoot.left
+ * ├── undershoot.right
  * ├── button.up
  * ├── entry
  * │   ╰── ...