Nat. Methods 14, 607–614 (2017); published online 1 May 2017; corrected after print 20 April 2018

In the version of this Article originally published, the wrong Protocol Exchange DOI and link (10.1038/protex.2017.047) were included in ref. 40. The URL in the reference should have been https://doi.org/10.1038/protex.2017.147. This error has been corrected in the HTML and PDF versions of the paper.