859: Fix typos - it's -> its r=cwfitzgerald a=ashpil
As I was reading the documentation, I found an instance where "it's" should actually be "its", as it is used as a possessive, not a contraction. I fixed that and `grep`ed for other instances, of which I found one and fixed as well.
Co-authored-by: ashpil <shpilenok2001@gmail.com>