It appears that the conventional-commits-parser package doesn't directly support the exclamation mark demarcation for noting a breaking change in a commit. Parsing the following commit measage:

chore!: drop node 8 support

Will yield a node with the following structure:

{
  type: null,
  scope: null,
  subject: null,
  merge: null,
  header: 'chore!: drop node 8 support',
  body: null,
  footer: null,
  notes: [],
  references: [],
  mentions: [],
  revert: null,
  hash: 'd0059c44727bd0562db42aedeed60713b698c264',
  breaking: false
}

A notable number of properties are left null in addition to not recognizing the ! indicating a breaking change. Support for ! is noted in the first item in the Specification https://www.conventionalcommits.org/en/v1.0.0/#specification.