Removed duplicate "are" in Contributing.md, issue #18
Pull Request Description
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__Licensing Certification__
FarmData2 is a [Free Cultural Work](https://freedomdefined.org/Definition) and all accepted contributions are licensed as described in the LICENSE.md file. This requires that the contributor holds the rights to do so. By submitting this pull request __I certify that I satisfy the terms of the [Developer Certificate of Origin](https://developercertificate.org/)__ for its contents.
Removed duplicate "are" in Contributing.md, issue #18
Pull Request Description