[gnome-software] trivial: Fix underlinking in the flatpak-system plugin

[Richard Hughes <rhughes src gnome org>]

commit 9bad6dd9b5ba2ce6f2c807bac8f3cb62905f4358
Author: Richard Hughes <richard hughsie com>
Date:   Thu Jun 2 15:45:50 2016 +0100

    trivial: Fix underlinking in the flatpak-system plugin

 src/plugins/Makefile.am |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/plugins/Makefile.am b/src/plugins/Makefile.am
index 2c025ad..c5389c2 100644
--- a/src/plugins/Makefile.am
+++ b/src/plugins/Makefile.am
@@ -166,6 +166,8 @@ if HAVE_FLATPAK
 libgs_plugin_flatpak_system_la_SOURCES =               \
        gs-appstream.c                                  \
        gs-appstream.h                                  \
+       gs-flatpak.c                                    \
+       gs-flatpak.h                                    \
        gs-plugin-flatpak-system.c
 libgs_plugin_flatpak_system_la_LIBADD = $(GS_PLUGIN_LIBS) $(FLATPAK_LIBS)
 libgs_plugin_flatpak_system_la_LDFLAGS = -module -avoid-version