fix issue #445

[gilbertogalvis]

This PR fix the issues in issue #445 posted

Example 1

h = histogram2(randn(1000,1),randn(1000,1),[12 12],'FaceColor','flat');
colorbar

fig2plotly(gcf);

Example 2

x = randn(1000,1);
y = randn(1000,1);
h = histogram2(x,y)

h.FaceColor = 'flat';

fig2plotly(gcf);

Example 3

x = randn(1000,1);
y = randn(1000,1);
h = histogram2(x,y)

h.FaceColor = 'flat';

h.NumBins = [10 25];

h.DisplayStyle = 'tile';
view(2)

fig2plotly(gcf);