npm audit command should check vendor directories

[diracdeltas]

fix #1853

note that this audit will fail until all the PRs i opened in the vendor
directories are merged. see
#1853 for references to
those PRs.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Requested a security/privacy review as needed.

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions.

[bbondy]

master: 6222bd3
0.57.x: 27776b0
0.56.x: 59a7b5d

[bbondy]

DEPS update commit merged here:
master: brave/brave-core@3120299
0.57.x: brave/brave-core@404a175
0.56.x: brave/brave-core@731719d