I don't know Julia, but maybe findfirst doesn't work well in 0.6?
I can confirm your problem is in that if, I've used some other methods there and made it work. Note that your code doesn't check for repeated values in array1 either.

...return a sorted array r in lexicographical order...

Yes.

Expected: ["he", "oint", "or", "ou", "wh"], instead got: ["he", "wh", "or", "oint", "ou"]. Really :(