Question: when did july 4 become a federal holiday
[{'answer': '1938', 'provenance': [{'wikipedia_id': '781729', 'title': 'Independence Day (United States)', 'start_paragraph_id': 15, 'start_character': 15, 'end_paragraph_id': 15, 'end_character': 19, 'bleu_score': 1.0, 'section': 'Section::::Observance.\n'}]}, {'provenance': [{'wikipedia_id': '781729', 'title': 'Independence Day (United States)', 'start_paragraph_id': 15, 'start_character': 0, 'end_paragraph_id': 15, 'end_character': 80, 'bleu_score': 0.8242367502646051, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 798912213801699027}, 'section': 'Section::::Observance.\n'}]}]