I don't know what to say about this, I feel +0.5.  The truth is that here it feels a bit odd, as it's in the second line, and this section starts off in a slightly different tone than what you expect.

On the other hand I hate it when reviewers point out that I use contractions in papers, or if somebody claims that the word "thing" is not appropriate for academic writing.  I believe you can't have a black and white rule for this. I wouldn't want to follow "academic" writing standards in the scikit-learn docs.

I'd love to hear more opinions about this.