add more recent mpl to the build tests
add more recent mpl to the build tests

jpinedaf/pyspeckit,keflavich/pyspeckit,e-koch/pyspeckit,jpinedaf/pyspeckit,low-sky/pyspeckit,low-sky/pyspeckit,e-koch/pyspeckit,pyspeckit/pyspeckit,pyspeckit/pyspeckit,keflavich/pyspeckit