[libchamplain] Add missing mapbox.py demo to Makefile.am

[Jiří Techet <jiritechet src gnome org>]

commit f506a0a120c1f30a5027c7615f65b213a1fc27f2
Author: Jiří Techet <techet gmail com>
Date:   Thu Feb 7 13:44:36 2019 +0100

    Add missing mapbox.py demo to Makefile.am

 demos/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/demos/Makefile.am b/demos/Makefile.am
index b74823a..496dffd 100644
--- a/demos/Makefile.am
+++ b/demos/Makefile.am
@@ -58,5 +58,5 @@ launcher_vala_LDADD = \
        $(top_builddir)/champlain/libchamplain-@CHAMPLAIN_API_VERSION@.la
 endif
 
-EXTRA_DIST = markers.h launcher.js minimal.py launcher-gtk.py polygons.py keyboard-mapping.py
+EXTRA_DIST = markers.h launcher.js minimal.py launcher-gtk.py polygons.py keyboard-mapping.py mapbox.py