chore(cli-lib-alpha): remove dependency on in-source compilation

An integration test of `cli-lib-alpha` expects a test compilation
`app.ts` -> `app.js` to have happened.

In new projen-based repos, this isn't going to work, since we don't
compile the test directories at all and run them through `ts-node`
instead. Configure the test to use `ts-node` as well.

packages/@aws-cdk/cli-lib-alpha/test/test-app/cdk.json

@@ -1,3 +1,3 @@
 {
-  "app": "node app.js"
+  "app": "ts-node app.ts"
 }