fix: yeoman generator

[mdonnalley]

What does this PR do?

Fixes issue with generate commands not being able to run:

~/code » sf dev generate plugin                                                            mdonnalley@mdonnal-ltmghj6
Error: Callback support have been removed.
    at Environment.run (/Users/mdonnalley/.local/share/sf/node_modules/yeoman-environment/lib/environment.js:979:13)
    at /Users/mdonnalley/.local/share/sf/node_modules/@salesforce/plugin-dev/lib/util.js:16:13
    at new Promise (<anonymous>)
    at generate (/Users/mdonnalley/.local/share/sf/node_modules/@salesforce/plugin-dev/lib/util.js:15:12)
    at GeneratePlugin.run (/Users/mdonnalley/.local/share/sf/node_modules/@salesforce/plugin-dev/lib/commands/dev/generate/plugin.js:16:35)
    at GeneratePlugin._run (/Users/mdonnalley/.local/share/sf/node_modules/@oclif/core/lib/command.js:81:33)

What issues does this PR fix or reference?

[skip-validate-pr]