setting clims forces colorbar with hat

[vascotenner]

When an image is plotted, with values that are not within the clims, the colorbar show a little hat on top/bottom.

However, when setting the clims to (None,None), the clims should be determined automatically and no hat should be shown:

Works

%%opts Image [colorbar=True]
tmp = np.random.rand(10,10)
tmp /= tmp.max()
hv.Image(tmp)

Works not

%%opts Image [colorbar=True] (clims=(None,None)) 
hv.Image(tmp)

[philippjfr]

Fixed in #1211.