Set citation data free

Read the full article at: https://www.nature.com/articles/d41586-019-02669-3?WT.ec_id=NATURE-20190912&utm_source=nature_etoc&utm_medium=email&utm_campaign=20190912&sap-outbound-id=BDA8AED77FFBB457D85C74FD91A0234CE42D6550&utm_source=hybris-campaign&utm_medium=email&utm_campaign=000_AGN6567_0000014844_41586-Nature-20190912-EAlert&utm_content=EN_internal_32879_20190912&mkt-key=005056B0331B1ED7838C3CBD38E18342