Fix node version in "Migration from v2"

Editor assessment

`docs: fix node version in the Migration from v2 guide` names the document and the corrected fact; for a version-number repair that is complete communication, and the quoted section title adds precision. Docs is the correct type, and no scope is needed for a README-adjacent tweak. No body — unnecessary for a factual correction — and the trailing PR reference is clean. Capitalized start is a permitted choice; length and punctuation are fine. The subject says what changed and where without any diff. A small, correct, fully legible example.