deps: bump ts-loader to support TS 4.7+

- due to a breaking change in TS 4.7 (TS does not follow SemVer), `ts-loader` needed an update: https://github.com/TypeStrong/ts-loader/blob/v9.4.4/CHANGELOG.md#v840

- `ts-loader` [v8](https://github.com/TypeStrong/ts-loader/blob/v9.4.4/CHANGELOG.md#v800)'s only breaking change was to no longer support TS <3.6

Signed-off-by: Anton Gilgur <agilgur5@gmail.com>

ui/package.json

@@ -74,7 +74,7 @@
         "source-map-loader": "^1.1.3",
         "style-loader": "^1.3.0",
         "ts-jest": "^26.4.4",
-        "ts-loader": "^7.0.4",
+        "ts-loader": "^8.4.0",
         "ts-node": "^9.1.1",
         "tslint": "^5.20.1",
         "tslint-config-prettier": "^1.18.0",