docs(changelog): add missing v7 breaking change (node 10+ → 18+)

[serhalp]

package.json#engines was changed from >=10 to >=18 in 7.0.0: https://github.com/isaacs/node-tar/commit/114c7ac4c24441cbe13de4aa46a864d46676c6bc#diff-7ae45ad102eab3b6d7e7896acd08c427a9b25b346470d7bc6507b6481575d519R43-R44.

This is a huge breaking change that should be documented in release notes.