Add ts-jest as a devDependency (#287)

Author: trivikr

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

@@ -6,7 +6,6 @@
     "clean": "yarn remove-definitions && yarn remove-dist && yarn remove-documentation",
     "build-documentation": "yarn remove-documentation && typedoc ./",
     "prepublishOnly": "yarn build",
-    "pretest": "yarn build:cjs",
     "remove-definitions": "rimraf ./types",
     "remove-dist": "rimraf ./dist",
     "remove-documentation": "rimraf ./docs",
@@ -34,6 +33,7 @@
     "jest": "^26.1.0",
     "rimraf": "^3.0.0",
     "typedoc": "^0.20.0",
+    "ts-jest": "^26.4.1",
     "typescript": "~4.1.2"
   },
   "engines": {