Should I include as co-author someone who helped me in modifying a journal paper based on a peer-review I have received?
You should consider it, I think, but there is too little information here to give a positive recommendation. It would depend on whether the other person contributed to the ideas at the heart of the paper. If they only gave advice on wording or presentation, then probably not.
Note that editors and even reviewers making suggestions don't become co-authors. You have to judge their contribution. But note that they may have an opinion about it that you should take into account as well.
But let me suggest something beyond pure accounting and ethical obligation. While this may not be true in some fields that depend on rigorous bean counting to rate people, I'd suggest a general view that you are generous rather than stingy can serve you well in the long run. If I were the commenter on your paper, I'd suggest that an acknowledgement is enough (or more than enough). If I were the author, I'd be more inclined to include the commentator than not, though the first part of this answer still applies. Over the course of your career it may matter little whether you are the sole or joint author of any given paper. But, having a wide circle of people willing to collaborate with you is a big plus in the long term.
But, if you are at the very beginning of your career and looking for a job, you might need a sole author publication at this moment. That depends on the field, I think. But I'd suggest short term thinking only if truly necessary.