Question: when last did nigeria win the african nations cup
[{'answer': '2013', 'provenance': [{'wikipedia_id': '38288476', 'title': '2013 Africa Cup of Nations Final', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 4, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]