[gnome-builder] build: Add missing header file

[Mathieu Bridon <mbridon src gnome org>]

commit 07c7ce7d032e34a3384fa1d52e1caa3c4c9d2a99
Author: Mathieu Bridon <bochecha daitauha fr>
Date:   Tue Dec 23 12:18:21 2014 +0100

    build: Add missing header file
    
    https://bugzilla.gnome.org/show_bug.cgi?id=741899

 src/gnome-builder.mk |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/gnome-builder.mk b/src/gnome-builder.mk
index 5cbda05..a6e1b08 100644
--- a/src/gnome-builder.mk
+++ b/src/gnome-builder.mk
@@ -59,6 +59,7 @@ libgnome_builder_la_SOURCES = \
        src/documents/gb-document-manager.h \
        src/documents/gb-document-menu-button.c \
        src/documents/gb-document-menu-button.h \
+       src/documents/gb-document-private.h \
        src/documents/gb-document-split.c \
        src/documents/gb-document-split.h \
        src/documents/gb-document-stack.c \