fix coco category id mismatch bug

Author: zylo117

efficientdet/dataset.py

@@ -73,7 +73,7 @@ def load_annotations(self, image_index):
 
             annotation = np.zeros((1, 5))
             annotation[0, :4] = a['bbox']
-            annotation[0, 4] = a['category_id']
+            annotation[0, 4] = a['category_id'] - 1
             annotations = np.append(annotations, annotation, axis=0)
 
         # transform from [x, y, w, h] to [x1, y1, x2, y2]