Make compatible with GLib < 2.36
Make compatible with GLib < 2.36

Gio.FileEnumerator.get_child() is too new for the version of GLib that
we currently install on Travis CI. Since this is the only incompatibility
and it's easily worked around, then we may as well work around it in
order to be compatible with earlier versions.

ptomato/jasmine-gjs,ptomato/jasmine-gjs