Question: when was thanksgiving changed to the fourth thursday
[{'answer': 'December 26 , 1941', 'provenance': [{'wikipedia_id': '8304348', 'title': 'Thanksgiving (United States)', 'start_paragraph_id': 50, 'start_character': 44, 'end_paragraph_id': 50, 'end_character': 62, 'bleu_score': 1.0, 'section': 'Section::::History.:1942 to present.\n'}]}, {'provenance': [{'wikipedia_id': '8304348', 'title': 'Thanksgiving (United States)', 'start_paragraph_id': 49, 'start_character': 0, 'end_paragraph_id': 49, 'end_character': 456, 'bleu_score': 0.639442406233179, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16242262003513260201}, 'section': 'Section::::History.:1942 to present.\n'}]}]