Please complete the following checklist:

* [ ] I have read the guidelines in [CONTRIBUTING.md](https://github.com/biocore/scikit-bio/blob/master/CONTRIBUTING.md).

* [ ] I have documented all public-facing changes in [CHANGELOG.md](https://github.com/biocore/scikit-bio/blob/master/CHANGELOG.md).

* [ ] **This pull request includes code, documentation, or other content derived from external source(s).** If this is the case, ensure the external source's license is compatible with scikit-bio's [license](https://github.com/biocore/scikit-bio/blob/master/COPYING.txt). Include the license in the `licenses` directory and add a comment in the code giving proper attribution. Ensure any other requirements set forth by the license and/or author are satisfied. **It is your responsibility to disclose code, documentation, or other content derived from external source(s).** If you have questions about whether something can be included in the project or how to give proper attribution, include those questions in your pull request and a reviewer will assist you.

* [ ] **This pull request does not include code, documentation, or other content derived from external source(s).**

**Note:** [REVIEWING.md](https://github.com/biocore/scikit-bio/blob/master/REVIEWING.md) may also be helpful to see some of the things code reviewers will be verifying when reviewing your pull request.
