Support promise.catch in exercise Reject a promise

[TylerYang]

In reject a promise exercise, we didn't support promise.then while catching the rejection. Check this link.

catch and then(null, handleError) are basically the same thing, and instead of doing promise.then(null, handleError), an experienced user would just use promise.catch(handleError). Like issue https://github.com/stevekane/promise-it-wont-hurt/issues/125.

I would like to send a pr if you think supporting promise.catch in reject a promise is reasonable. Looking forward to your opinion.

[TimothyGu]

Sure, a patch would be welcome.