cli-ux is deprecated

[jfirebaugh]

When installing this package, or any package that depends on it, npm prints the following warning:

npm WARN deprecated cli-ux@5.6.7: Package no longer supported. Contact Support at https://www.npmjs.com/support for more info.

This is because cli-ux, which this package depends on, has been deprecated and is now unmaintained. The replacement is @oclif/core, see this document for upgrade instructions.