**Please do not work on this issue unless you have applied to the outreachy project.**

The [jpeg_viewer.js](https://github.com/mozilla/pdf.js/blob/master/examples/image_decoders/jpeg_viewer.js) example currently uses the older style of `promise.then` and callbacks. Convert it to use an `async` function and `await` style.

/* Copyright 2018 Mozilla Foundation
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 * Licensed under the Apache License, Version 2.0 (the "License");
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