CONTRIBUTING: match quantifier with actual number of items in the list

[vanschelven]

No description provided.

[vanschelven]

I fully understand that this is an entirely trivial change, but you "gotta start somewhere";

alternatively, I can imagine that there's actually a third group missing from the enumeration below, or that the enumeration should be split up differently. In that case, just close my PR

[nicolo-ribaudo]

@vanschelven Thank you for your PR! Could you fill https://tc39.es/agreements/contributor/?

[vanschelven]

I just did