Question: when was the last time washington redskins won a superbowl
[{'answer': '1991', 'provenance': [{'wikipedia_id': '33673', 'title': 'Washington Redskins', 'start_paragraph_id': 4, 'start_character': 210, 'end_paragraph_id': 4, 'end_character': 214, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]