Remove lines from contour plot

I have this matrix for which I want to create a contour plot:

M = [[np.exp(-(i-j)**2/100) for i in range(100)] for j in range(100)]

I know how to create the contour plot:

fig = go.Figure()
fig.add_contour(z=M, contours_coloring='heatmap', contours_showlines=False)

But, how can I remove the contour lines? contours_showlines=False does not appear to work.

I had the same problem in R plotly.

Try add
line = list(width = 0)