[gnome-games] build: Make .flatpak-builder a maintainerclean target

[Adrien Plazas <aplazas src gnome org>]

commit a919b2686031efba1f523db11641d0bae72bb581
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Mar 29 14:54:10 2017 +0200

    build: Make .flatpak-builder a maintainerclean target
    
    This avoids having the content of .flatpak-builder as Git untracked
    files.

 Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 614d3e7..e437e07 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,6 +5,7 @@ SUBDIRS = data po src plugins
 MAINTAINERCLEANFILES = \
        $(GITIGNORE_MAINTAINERCLEANFILES_TOPLEVEL) \
        $(GITIGNORE_MAINTAINERCLEANFILES_MAKEFILE_IN) \
+       .flatpak-builder \
        $(NULL)
 
 -include $(top_srcdir)/git.mk