COMET metric citation
I think its better to create a new branch with this fix. I forgot I was still using the old branch.
In my last pull request to add COMET metric, the citations where not following the usual "format". Because of that they where not correctly displayed on the website: 

<img width="814" alt="Screenshot 2021-01-20 at 09 48 44" src="https://user-images.githubusercontent.com/17256847/105158000-686efb80-5b05-11eb-8bb0-9c85fdac2938.png">

This pull request is only intended to fix that.