Typo in split_chain.R

[bdhumb]

There is a typo here where it says myst instead of must. I don't particularly want to figure out how to update it myself and get it merged in but maybe someone who contributes has 1 minute to fix it?

[Bisaloo]

@bdhumb, I just had a look and this has actually been fixed in e95aa63 (5 years ago). There just hasn't been a release on CRAN since then.