My sister has only daughters, my mom has only sisters, half of my aunts only have daughters, my grandmother only has sisters... I've heard them say "miss you guys" to each other more times in my life than I can count... it's gender neutral enough.
In fact, I have yet to see an actual *woman* take offense to this phrase, it's always some SJW man that seems over-sensitive to it. I saw someone bring it up in #node.js over someone asking "mind if I ask you guys a question?" once. Everyone seemed to kowtow to the statement, I think I'm the only one in the channel that challenged it and stand by that assertion. If someone decides that the word "roses" is suddenly offensive, it shouldn't be society that necessarily adapts.
Personally, I find the term "git" pretty offensive, but I'm not championing changing the name. The biggest irony is when "github" forced the change of a repo that had a term deemed offensive... There's a matter of intent and context to consider... "Only guys will get it, chicks just can't understand." would be offensive, and I understand that... in this context it's used as a generic pronoun.
I self-identify as a 68yo Black Lesbian Woman whose personal pronoun is "my lord and master".
I think "guy" is quite neutral, and also "dude", and *also* "man" in neutral contexts (i.e., not opposed to "woman"), but still this isn't about JavaScript.
Could be that in the project maintainer's country of origin, "guy" is not neutral. From his profile it looks like he's from Germany. I don't think this event is worth much "note" though.