Hi,
thank you for trying and writing the error message. Yes, I tried it and getting the same error. Within Julia the package "BioSequences" is used and has updated since writing the instructions. So, it only works with BioSequences version 2.0.5.
I will update the article, however please try it again using the older version of "BioSequences":
1) Open Julia in the terminal
2) Type: ] to enter the package manager
3) add the older package by typing: add BioSequences@2.0.5
Maybe remove first the newest version within the package manger, type: rm Biosequences
Now it should work...