fix comet citations
I realized COMET citations were not showing in the hugging face metrics page:

<img width="814" alt="Screenshot 2021-01-20 at 09 48 44" src="https://user-images.githubusercontent.com/17256847/105164848-8b9da900-5b0d-11eb-9e20-a38f559d2037.png">

This pull request is intended to fix that.

Thanks!