Periodically and automatically update environment-colab.yml

[icoxfog417]

As a data scientist who want to save Colab notebook with reproducable environment, the environment-colab.yml should follow the latest Colab environment. To enable this, the cycle to update environment-colab.yml periodically and automatically is required.

The rough procedures are the following:

1. Make latest package list by executing pip freeze on Colab periodically (by using Colab Pro+ feature?).
2. Make the latest environment-colab.yml from the 1) and packages listed on existing environment-colab.yml.
3. Make the latest requirements-colab.txt from 1) and 2) .
4. git add/commit/push 2) and 3) to this repository