updates tomcat action with sources output

[pivotal-david-osullivan]

Summary

Adds support for source fields to be output by the action, for use in update-buildpack-dependency workflows

See apache-tomcat#377

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
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• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).