Update public_suffix gem to 1.4.6

## What? Why?
Bumps the public_suffix gem to the latest version to allow the latest TLDs to be used.

This PR:
* Updates the public_suffix gem to the latest tagged version (1.4.6)
* Adds a new test that given a TLD from the latest public_suffix definitions file (https://github.com/weppos/publicsuffix-ruby/commit/df4b9e0d47dd575b2c5bda6088c5687d6a92b550#diff-6af66fb96ba3676c54785b92b8e0462f), confirms the domain can be parsed. An error similar to ```PublicSuffix::DomainInvalid: `test123456test123456.beer' is not a valid domain``` will be generated if the TLD isn't recognized by public_suffix.

## Additional Deploy Steps?
* Depends on bigcommerce-labs/enom#1 being merged first so the test suite will run.


## How was it tested?
```bundle exec rake```

cc @IamDavidovich @splittingred @jlleblanc @charrisbc