chore: upgrade typescript to 3.8.3 (#1641)

Author: JoelEinbinder

package.json

@@ -77,7 +77,7 @@
     "pixelmatch": "^4.0.2",
     "text-diff": "^1.0.1",
     "ts-loader": "^6.1.2",
-    "typescript": "^3.7.5",
+    "typescript": "^3.8.3",
     "webpack": "^4.41.0",
     "webpack-cli": "^3.3.9"
   },