Model card generation fails due to image too large

## Expected Behavior
Model card generation fails due to the histogram to large.

## Actual Behavior
`_draw_histogram` calls `figure_to_base64str`. 
The method calls `fig.savefig(buf, bbox_inches='tight', format='png')` 

The save fails with 
```
ValueError: Image size of 6440035x455 pixels is too large. It must be less than 2^16 in each direction.
```
