chore: bump vega-lite-dev-config from 0.18.0 to 0.21.0

Bumps [vega-lite-dev-config](https://github.com/vega/vega-lite-dev-config) from 0.18.0 to 0.21.0.
- [Release notes](https://github.com/vega/vega-lite-dev-config/releases)
- [Changelog](https://github.com/vega/vega-lite-dev-config/blob/v0.21.0/CHANGELOG.md)
- [Commits](vega/vega-lite-dev-config@v0.18.0...v0.21.0)

---
updated-dependencies:
- dependency-name: vega-lite-dev-config
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -76,7 +76,7 @@
     "typescript": "^4.0.5",
     "typescript-json-schema": "^0.51.0",
     "vega-datasets": "latest",
-    "vega-lite-dev-config": "^0.18.0"
+    "vega-lite-dev-config": "^0.21.0"
   },
   "dependencies": {
     "datalib": "~1.9.3",