build(deps): bump @googlemaps/url-signature from 1.0.20 to 1.0.21 (#798)

Bumps [@googlemaps/url-signature](https://github.com/googlemaps/js-url-signature) from 1.0.20 to 1.0.21.
- [Release notes](https://github.com/googlemaps/js-url-signature/releases)
- [Commits](googlemaps/js-url-signature@v1.0.20...v1.0.21)

---
updated-dependencies:
- dependency-name: "@googlemaps/url-signature"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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