Bump underscore from 1.13.6 to 1.13.7 (#533)

Bumps [underscore](https://github.com/jashkenas/underscore) from 1.13.6 to 1.13.7.
- [Commits](jashkenas/underscore@1.13.6...1.13.7)

---
updated-dependencies:
- dependency-name: underscore
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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