Question: when was the last time novak djokovic won a grand slam
[{'answer': '2018', 'provenance': [{'wikipedia_id': '16100029', 'title': 'Novak Djokovic', 'start_paragraph_id': 95, 'start_character': 11, 'end_paragraph_id': 95, 'end_character': 15, 'bleu_score': 1.0, 'section': 'Section::::Tennis career.:2017: Split with team and long injury hiatus.\n'}]}]