chore(deps): update dependency typescript to v4 (#297)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

package-lock.json

@@ -121,7 +121,7 @@
     "sinon": "9.0.3",
     "snap-shot-it": "7.9.3",
     "tmp-promise": "3.0.2",
-    "typescript": "3.9.7"
+    "typescript": "4.0.2"
   },
   "collective": {
     "type": "opencollective",