Bump up doc node version to 16
Author: mishig25
Pull request: yes

# What does this PR do?

Fixed the doc-build issue we disucssed by bumping up node 14 -> 16

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Comments:
@LysandreJik this should fix the CI issue in https://github.com/huggingface/transformers/pull/15710

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15874). All of your documentation changes will be reflected on that endpoint.