chore(#41): Lock TypeScript version

Author: iainjreid

package.json

@@ -65,7 +65,7 @@
     "prettier": "^2.2.1",
     "rimraf": "^3.0.2",
     "ts-node": "^9.1.0",
-    "typescript": "^4.1.2"
+    "typescript": "4.1.2"
   },
   "peerDependencies": {
     "ts-node": ">=9.0.0"