Question: when was the last time steelers won a superbowl
[{'answer': '2008', 'provenance': [{'wikipedia_id': '23338', 'title': 'Pittsburgh Steelers', 'start_paragraph_id': 20, 'start_character': 1013, 'end_paragraph_id': 20, 'end_character': 1017, 'bleu_score': 1.0, 'section': 'Section::::Franchise history.:The Mike Tomlin era.\n'}]}]