Bump chart.js from 2.8.0 to 2.9.4

Bumps [chart.js](https://github.com/chartjs/Chart.js) from 2.8.0 to 2.9.4.
- [Release notes](https://github.com/chartjs/Chart.js/releases)
- [Commits](chartjs/Chart.js@v2.8.0...v2.9.4)

---
updated-dependencies:
- dependency-name: chart.js
  dependency-type: direct:production
...

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

package.json

@@ -37,7 +37,7 @@
   "homepage": "https://smariel.github.io/PTree",
   "dependencies": {
     "bootstrap": "^3.4.1",
-    "chart.js": "v2.8",
+    "chart.js": "v2.9",
     "fabric": "^4.6.0",
     "font-awesome": "^4.7.0",
     "jquery": "^3.6.0",