Bump chart.js from 2.7.1 to 2.9.4 (#592)

Bumps [chart.js](https://github.com/chartjs/Chart.js) from 2.7.1 to 2.9.4.
- [Release notes](https://github.com/chartjs/Chart.js/releases)
- [Commits](chartjs/Chart.js@v2.7.1...v2.9.4)

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

@@ -30,7 +30,7 @@
         "@types/jasmine": "2.5.53",
         "@types/jasminewd2": "2.0.2",
         "@types/node": "6.0.60",
-        "chart.js": "2.7.1",
+        "chart.js": "2.9.4",
         "codelyzer": "4.0.1",
         "core-js": "2.4.1",
         "del": "2.2.0",