if private module don't append `--tag prerelease`

[whyvez]

standard-version 4.4.0

I've run into an issue with a prerelease for a private module where the --tag prerelease npm publish option was appended to the final git push help text.

✔ bumping version in package.json from 1.2.0-beta.4 to 1.2.0-dev.0
✔ bumping version in package-lock.json from 1.2.0-beta.4 to 1.2.0-dev.0
✔ outputting changes to CHANGELOG.md
✔ committing package-lock.json and package.json and CHANGELOG.md
✔ tagging release v1.2.0-dev.0
ℹ Run `git push --follow-tags origin master --tag prerelease` to publish

Need to wrap this logic within the if (pkgPrivate !== true) condition.

refs: #183 (reference)

[stevemao]

Thanks @whyvez , must be a bug.