Bump typescript to ~4.0.2 (#203)

Author: trivikr

smithy-typescript-codegen/src/main/resources/software/amazon/smithy/typescript/codegen/base-package.json

@@ -32,7 +32,7 @@
     "jest": "^26.1.0",
     "rimraf": "^3.0.0",
     "typedoc": "^0.17.8",
-    "typescript": "~3.9.3"
+    "typescript": "~4.0.2"
   },
   "engines": {
     "node": ">=8.0.0"