Google Colab link points to a non existant page

[louis1204]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://finrl.readthedocs.io/en/latest/tutorial/Introduction/SingleStockTrading.html
2. Click on 'Run the code step by step at Google Colab.'
3. See error

Expected behavior
Expect to link to a valid page.