[BUG] "Run in Colab" button in tutorials not working

[matteobettini]

The "Run in Colab" button of the notebooks seems to give an error

Notebook not found
There was an error loading this notebook. Ensure that the file is accessible and try again.
https://github.com/pytorch/rl/blob/gh-pages/_downloads/c4cc1ccac40ca535b79628b7eb0bbe18/coding_ppo.py
Fetch for https://api.github.com/repos/pytorch/rl/contents/_downloads/c4cc1ccac40ca535b79628b7eb0bbe18?per_page=100&ref=gh-pages failed: {
  "message": "Not Found",
  "documentation_url": "https://docs.github.com/rest/repos/contents#get-repository-content"
}

CustomError: Fetch for https://api.github.com/repos/pytorch/rl/contents/_downloads/c4cc1ccac40ca535b79628b7eb0bbe18?per_page=100&ref=gh-pages failed: {
  "message": "Not Found",
  "documentation_url": "https://docs.github.com/rest/repos/contents#get-repository-content"
}

    at new EO (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:2493:68)
    at ua.program_ (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:2476:435)
    at za (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:16:57)
    at ua.next_ (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:14:195)
    at kaa.next (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:17:48)
    at b (https://ssl.gstatic.com/colaboratory-static/common/78fd4640f7d67f94e8a68d0d5bbcdea9/external_polymer_binary.js:17:309)

It seems due to the fact that it is not able to load the artifact from https://api.github.com/repos/pytorch/rl/contents/_downloads/c4cc1ccac40ca535b79628b7eb0bbe18?per_page=100&ref=gh-pages