jspm sample is out of date

[aluanhaddad]

The jspm sample uses TypeScript 1.8.10 and plugin-typescript 4.0.6.
It should be updated to demonstrate use with the latest versions.
Furthermore, while the sample contains a tsconfig.json, which can be read by an IDE, it is not used being passed to configure plugin-typescript to match. Demonstrating this would be useful and helps explain the relationship between TypeScript and plugin-typescript.
The tsconfig.json file should be used as per #20

[DanielRosenwasser]

We'd absolutely be willing to take a PR, and I think you would probably know what best practices to follow on this. 😃

[aluanhaddad]

@DanielRosenwasser thanks!

[DanielRosenwasser]

Thanks for the PR!