bug: `-t` flag does not accept the new `targetId[targetName]` format

Initially reported by @jan-auer on Slack:

```shell
craft publish 0.3.0 -t gcs -t 'release[docker]' -t 'latest[docker]'
Invalid values:
  Argument: target, Given: "release[docker]", "latest[docker]", Choices: "brew", "cocoapods", "crates", "docker", "gcs", "gem", "gh-pages", "github", "npm", "nuget", "pypi", "registry", "all", "none"
```

This is a fallout from #128.