Bump bootstrap from 4.5.0 to 4.6.0 in /frontend

Bumps [bootstrap](https://github.com/twbs/bootstrap) from 4.5.0 to 4.6.0.
- [Release notes](https://github.com/twbs/bootstrap/releases)
- [Commits](twbs/bootstrap@v4.5.0...v4.6.0)

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

frontend/package.json

@@ -39,13 +39,13 @@
     "prettier": "^2.1.2",
     "sass-loader": "^8.0.2",
     "sirv-cli": "^1.0.6",
-    "ts-loader": "^7.0.5",
+    "ts-loader": "^8.0.17",
     "typescript": "^3.9.5"
   },
   "dependencies": {
-    "bootstrap": "^4.5.0",
+    "bootstrap": "^4.6.0",
     "preact": "^10.4.4",
-    "preact-render-to-string": "^5.1.9",
+    "preact-render-to-string": "^5.1.13",
     "preact-router": "^3.2.1",
     "react-smooth-dnd": "^0.11.1"
   }