Question: when was the last time there was a nba finals sweep
[{'answer': '2018', 'provenance': [{'wikipedia_id': '890793', 'title': 'NBA Finals', 'start_paragraph_id': 51, 'start_character': 91, 'end_paragraph_id': 51, 'end_character': 95, 'bleu_score': 1.0, 'section': "Section::::History.:2015–present: Warriors' dynasty.\n"}]}, {'provenance': [{'wikipedia_id': '890793', 'title': 'NBA Finals', 'start_paragraph_id': 54, 'start_character': 0, 'end_paragraph_id': 54, 'end_character': 981, 'bleu_score': 0.7472842474914441, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1649746545553282551}, 'section': "Section::::History.:2015–present: Warriors' dynasty.\n"}]}]