Puppet 8 support

[alvagante]

Before submitting your PR

1. Open an issue and refer to its number in your PR title
2. If it's a bug and you have the solution, go on with the PR!
3. If it's an enhancement, please wait for our feedback before starting to work on it
4. Please run puppet-lint on your code and ensure it's compliant

After submitting your PR

1. Verify Travis checks and eventually fix the errors
2. Feel free to ping us if we don't reply promptly

[github-advanced-security]

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