Bump typescript from 3.9.7 to 4.0.2 in /Rnwood.Smtp4dev/ClientApp (#443)

Bumps [typescript](https://github.com/Microsoft/TypeScript) from 3.9.7 to 4.0.2.
- [Release notes](https://github.com/Microsoft/TypeScript/releases)
- [Commits](microsoft/TypeScript@v3.9.7...v4.0.2)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Rnwood.Smtp4dev/ClientApp/package.json

@@ -30,7 +30,7 @@
     "moment": "^2.27.0",
     "srcdoc-polyfill": "^1.0.0",
     "ts-debounce": "^2.0.1",
-    "typescript": "~3.9.7",
+    "typescript": "~4.0.2",
     "vue-router": "^3.4.3",
     "vue-template-compiler": "^2.6.12",
     "vue2-ace-editor": "0.0.15",