Fix missing tsloader return statement

[ldiringer]

This commit (35d9e6f#diff-168726dbe96b3ce427e7fedce31bb0bc) removed inadvertently the return this; statement from the enableTypeScriptLoader function.

This prevents calling another function chained on enableTypeScriptLoader in a webpack.config.js file.

This PR just puts the return this; statement back.

[davidmpaz]

We should definitely make a test for the pubic API, to prevents such cases in future. Do you think you could add some @ldiringer ?

[davidmpaz]

what do you think if api.js file get renamed to index.js, that way it explicitly says what part is testing?

tests look great!. Thank you very much, i hope this get merged soon.

[ldiringer]

All done. Thank you for the review @davidmpaz!

[weaverryan]

Thank you @ldiringer.

[weaverryan]

And thank you also for the test - that was very clearly needed.