fix issue related to bar functionality

[gilbertogalvis]

Description of the issue

I'm trying a grouped bar plot:

clear all;close all;

x = categorical({'Apples', 'Oranges', 'Bananas'});
y = [2 2 3; 2 5 6; 2 8 9; 2 11 12];
bar(x,y)
shg

fig = fig2plotly(gcf, 'offline', true, 'open', false,'Visible',false);

response = plotlyoffline(fig);

web(response, '-browser');

When showing the image with shg shows the correct plot, but fig2plotly shows clear axes.
I think there is some issue with categorical variables?

Issue fixed

This PR fix the previous explained issue. So Using the example code we can get following