Update unicode-display_width dependency

[KieranP]

Describe the change

Support using v3 of unicode-display_width

Why are we doing this?

Inline with rubocop requirements, so that we're not forcing users to downgrade

Benefits

Allow users of tty-progressbar to use latest gem versions

Drawbacks

None known

Requirements

• [x] Tests written & passing locally?
• [x] Code style checked?
• [x] Rebased with master branch?
• [x] Documentation updated?
• [x] Changelog updated?

[KieranP]

In a strict sense, the current constraints don't require any downgrade action on the user unless they are intent on using the very lastest unicode-display_width gem version. Usually, this is a transitory dependency, and most users probably don't use it directly.

True, however as a maintainer of an app that handles PII, it's always best to have all dependencies be on the latest version with security/bug fixes. Requiring a downgrade for a dependency in order to install latest versions of something we need is not an ideal compromise.

I'd also appreciate a change note in the changelog. This can be under ## unreleased and ### Changed headings.

Done