Setting a matplotlib.colors normalization as bounds causes error in mapcombined #47

import psyplot.project as psy
from matplotlib.colors import Normalize

combined = psy.plot.mapcombined(
    'les_toscana_test_icon_oper_DOM03_ML.nc',
    time=1,
    name=[['t_2m', ['u_10m', 'v_10m']]],
    bounds=Normalize(vmin=280, vmax=310),
    cmap='gist_ncar',
    vplot='stream',
    )

Plotter.__init__(self, data, ax, auto_update, project, draw, make_plot, clear, enable_post, **kwargs)
   1258 for key, value in six.iteritems(kwargs):  # then the user values
   1259     self[key] = value
-> 1260 self.initialize_plot(data, ax=ax, draw=draw, clear=clear,
...
--> 469     data = data.to_series()
    470 mask = np.asarray(data.notnull())
    471 return data.values[mask]
AttributeError: 'InteractiveList' object has no attribute 'to_series'