Hi! I can reproduce, and think it's being a bit too strict.
For now, use the shorter version of the map function:
return this.state.comments.map( (e) => e.avatarUrl );
e and the 1-"lined-ness" aren't the important parts, but the concise body version is.
Going to quickly double-check that your is the same as mine, which I think it is, and will then report an issue to improve this.
Thanks for posting!
update: yup, they be the same, so will make an issue to improve this and allow the lengthier version, too.