Throws returns the promise

[SamVerschueren]

Finally found the solution for #123

By returning the promise, it's possible to check the throwed error like this which succesfully waits untill the promise is resolved/rejected.

test(async t => {
    await t.throws(throws(), /hello world/);

    function throws() {
        return new Promise(function (resolve, reject) {
            setTimeout(function () {
                reject(new Error('hello world'));
            }, 2000);
        });
    }
});

[vadimdemedes]

lgtm

@sindresorhus?

[sindresorhus]

Looks good :)