Correct the naming conventions for the browser list config

[jimmynotjim]

Steven pointed out that the constants should be formatted in caps with
underscore separators.

Testing

1. Run gulp clean
2. Run gulp build
3. Run gulp scripts:ondemand

Everything should build and none of the site styles or interactions should differ in any browsers.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the development playbook
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged
• Visually tested in supported browsers and devices
• Project documentation has been updated
• Reviewers requested with the Reviewer tool ➡️