Fix sorting precision by confidence scores

When sorting a float number as text, strings like '1.0169535613613334e-07' will not be interpreted as expected.

main.py

@@ -407,7 +407,7 @@ def draw_plot_func(dictionary, n_classes, window_title, plot_title, x_label, out
         bounding_boxes.append({"confidence":confidence, "file_id":file_id, "bbox":bbox})
         #print(bounding_boxes)
   # sort predictions by decreasing confidence
-  bounding_boxes.sort(key=lambda x:x['confidence'], reverse=True)
+  bounding_boxes.sort(key=lambda x:float(x['confidence']), reverse=True)
   with open(tmp_files_path + "/" + class_name + "_predictions.json", 'w') as outfile:
     json.dump(bounding_boxes, outfile)