[roosterteeth] Allow bonus_feature_image as thumbnails

Certain bonus episodes do not have their thumbnail taged with
"episode_image", but as "bonus_feature_image".

youtube_dl/extractor/roosterteeth.py

@@ -109,7 +109,7 @@ class RoosterTeethIE(InfoExtractor):
 
         thumbnails = []
         for image in episode.get('included', {}).get('images', []):
-            if image.get('type') == 'episode_image':
+            if image.get('type') in {'episode_image', 'bonus_feature_image'}:
                 img_attributes = image.get('attributes') or {}
                 for k in ('thumb', 'small', 'medium', 'large'):
                     img_url = img_attributes.get(k)