fix: remove redundant .then() causing unhandled exception

[garymathews]

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Fixes #1547 🦕

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I'm not sure why .then() was added here, it appears to be redundant. But without chaining it will cause an unhandled exception; which is causing #1547.

Here's an example of an uncaught exception being thrown when chaining isn't used:

const promise = new Promise((resolve, reject) => {
    reject();
});

promise.then(() => console.log('resolved'));
promise.catch(e => console.error('rejected'));

rejected
node:internal/process/promises:288
            triggerUncaughtException(err, true /* fromPromise */);
            ^

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "undefined".] {
  code: 'ERR_UNHANDLED_REJECTION'
}

[viniychuk]

It works! Please merge it!

[garymathews]

CC @feywind @alexander-fenster @hongalex

I'd say this is a high priority issue, since without an unhandledException handler the app will just terminate upon receiving an error during an ack

[feywind]

@garymathews Apologies, I've been OoO and I'm the main maintainer. Hopefully we can get this in quickly.

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