fix: update closure file test to include more src files

[frederickfogerty]

Description

This PR updates the webpack and closure config to ensure that all src files are included. The closure plugin we use has a test flag that didn't work initially as I thought, so after investigating this I was able to fix it. As a side-effect of this update, the bundle size is even smaller at 10KB, an improvement of 46% over the original bundle size.

This fixes #75

Bug Fix

• All existing unit tests are still passing (if applicable)
• [N/A] Add new passing unit tests to cover the code introduced by your PR
• [N/A] Update the readme
• [N/A] Update or add any necessary API documentation
• Add some steps so we can test your bug fix
• The PR title is in the conventional commit format: e.g. fix(<area>): fixed bug #issue-number
• Add your info to the contributors array in package.json!

Steps to Test

IE 11

Steps:

1. Check that CI passes