Fix manifest containing the wrong no-autodownload value

Fix copy/paste error that made the "no-autodownload" value in
/app/manifest.json, showing the "autodelete" value instead.

Fixes: c6ef29c ("builder: Add support for defining extensions in flatpak-builder"

Author: hadess

src/builder-extension.c

@@ -127,7 +127,7 @@ builder_extension_get_property (GObject    *object,
       break;
 
     case PROP_NO_AUTODOWNLOAD:
-      g_value_set_boolean (value, self->autodelete);
+      g_value_set_boolean (value, self->no_autodownload);
       break;
 
     case PROP_LOCALE_SUBSET: