Bump @backstage/theme from 0.2.19 to 0.4.1

Bumps [@backstage/theme](https://github.com/backstage/backstage/tree/HEAD/packages/theme) from 0.2.19 to 0.4.1.
- [Release notes](https://github.com/backstage/backstage/releases)
- [Changelog](https://github.com/backstage/backstage/blob/master/packages/theme/CHANGELOG.md)
- [Commits](https://github.com/backstage/backstage/commits/v0.4.1/packages/theme)

---
updated-dependencies:
- dependency-name: "@backstage/theme"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -34,7 +34,7 @@
     "@backstage/core-components": "^0.13.3",
     "@backstage/core-plugin-api": "^1.3.0",
     "@backstage/errors": "^1.1.4",
-    "@backstage/theme": "^0.2.16",
+    "@backstage/theme": "^0.4.1",
     "@material-table/core": "v3.1.0",
     "@material-ui/core": "^4.12.2",
     "@material-ui/icons": "^4.9.1",