[udemy] Use chapter_number

youtube_dl/extractor/udemy.py

@@ -245,7 +245,7 @@ class UdemyCourseIE(UdemyIE):
             course_id, 'Downloading course curriculum')
 
         entries = []
-        chapter, chapter_id = None, None
+        chapter, chapter_number = None, None
         for asset in response:
             asset_type = asset.get('assetType') or asset.get('asset_type')
             if asset_type == 'Video':
@@ -256,13 +256,13 @@ class UdemyCourseIE(UdemyIE):
                         'url': 'https://www.udemy.com/%s/#/lecture/%s' % (course_path, asset['id']),
                         'ie_key': UdemyIE.ie_key(),
                     }
-                    if chapter_id:
-                        entry['chapter_id'] = chapter_id
+                    if chapter_number:
+                        entry['chapter_number'] = chapter_number
                     if chapter:
                         entry['chapter'] = chapter
                     entries.append(entry)
             elif asset.get('type') == 'chapter':
-                chapter_id = asset.get('index') or asset.get('object_index')
+                chapter_number = asset.get('index') or asset.get('object_index')
                 chapter = asset.get('title')
 
         return self.playlist_result(entries, course_id, course_title)