R4R: Add vendor-deps to .gitignore

[cwgoes]

cc @alessio

Doesn't need PENDING.md.

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added entries in PENDING.md with issue #
• rereviewed Files changed in the github PR explorer

---

For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[jackzampolin]

Plz

[codecov]

Codecov Report

Merging #3381 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #3381   +/-   ##
========================================
  Coverage    58.88%   58.88%           
========================================
  Files          131      131           
  Lines         9808     9808           
========================================
  Hits          5775     5775           
  Misses        3658     3658           
  Partials       375      375