Bump vega-interpreter from 1.2.0 to 1.2.1 (#249)

Bumps [vega-interpreter](https://github.com/vega/vega) from 1.2.0 to 1.2.1.
- [Release notes](https://github.com/vega/vega/releases)
- [Commits](https://github.com/vega/vega/commits)

---
updated-dependencies:
- dependency-name: vega-interpreter
  dependency-version: 1.2.1
  dependency-type: indirect
...

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