Oh, it seems that the compat declaration for Julia is wrong 
I have really only tested the package on the latest version of Julia, which was 1.4 at the time. I used to try to maintain compat with older Julia versions, but noticed that it took a lot of my bandwidth for little gain and decided to not pursue that anymore.
If you鈥檙e interested in distances between spectra, you may also be interested in the examples over at