Results 1 issues of June

https://github.com/yfpeng/object_detection_metrics/blob/7640436e65b85dc39773ba16350ab73327f2d3bb/src/podm/visualize.py#L48 '+' doesn't seem to append numpy arrays, suggestion: ``` area_under_curve_x = mrec[:-1].tolist() + [mrec[-2]] + [mrec[-1]] area_under_curve_y = mpre[:-1].tolist() + [0.0] + [mpre[-1]] ```