AttributeError: 'module' object has no attribute 'Vega20' for austechia.ipynb

AttributeError Traceback (most recent call last)
in ()
14 # tree_names=['PB1t','HAt'] ## define order that plots two trees
15
---> 16 cmap=mpl.cm.Vega20 ## choose a colour map
17 vega_colours={tree:[cmap((t2)/20.0),cmap((t2+1)/20.0)] for t,tree in enumerate(tree_names)}
18

AttributeError: 'module' object has no attribute 'Vega20'