docs: CDK usage suggests passing roleArn, but step function properties expects role

[dmeehan1968]

Here is the current docs for using TypescriptStateMachine:

new ts2asl.TypescriptStateMachine(this, "TypescriptStateMachine", {
  programName: "hello-world",
  defaultFunctionProps: {},
  defaultStepFunctionProps: {
    stateMachineType: "EXPRESS",
    roleArn: executionRole.roleArn
  },
  sourceFile: "./src/program.ts",
});

roleArn is not a propery of defaultStepFunctionProps, and should instead read:

role: executionRole