Refactor index.js to async/await

[tamasmuncsan]

Description

index.js is now using async/await instead of Promise chaining.

reference: https://github.com/cjwilburn/dank-memes/issues/58

Checklist

• [x] I have tested these code changes and included the relevant urls and screenshots.
• [x] I have updated our build tasks accordingly (if applicable).
• [x] I have updated our documentation accordingly (if applicable).
• [x] I have linted the code that I've included in this PR (if applicable).
• [x] My code follows the code style of this project.
• [x] My code is ready for review.