Correction to: https://doi.org/10.1038/s41556-019-0310-9, published online 29 April 2019
In the version of the article originally published, extra lines were displayed in Fig. 7. Fig. 7a contained a solid black line that extended into panel b, and Fig. 7c contained two extra scale bars on the left. These have been removed from the figure. The errors have been corrected in the HTML and PDF versions of the article.