Question: when did clan wars start in clash royale
[{'answer': 'April 25 , 2018', 'provenance': [{'wikipedia_id': '49103664', 'title': 'Clash Royale', 'start_paragraph_id': 16, 'start_character': 11, 'end_paragraph_id': 16, 'end_character': 32, 'bleu_score': 1.0, 'section': 'Section::::Gameplay.:Clan Wars.\n'}]}, {'provenance': [{'wikipedia_id': '49103664', 'title': 'Clash Royale', 'start_paragraph_id': 16, 'start_character': 0, 'end_paragraph_id': 16, 'end_character': 387, 'bleu_score': 0.8917581509113751, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12129677391670025040}, 'section': 'Section::::Gameplay.:Clan Wars.\n'}]}]