Update the python version and some other packages

[YoshikiOhtani]

With this pull request I updated the python version to 3.8 to use a new feature, and accordingly other packages. Removing the requirement on bokeh is needed to update the python version, and regarding sphinx I just let it follow the requirement of the other packages. For the other packages I just updated the versions. @aleberti could you please have a look? Thanks in advance.

[aleberti]

As we discussed via Slack, if the environment installs fine, I guess there are no problems in merging.

[aleberti]

Maybe about the lstchain version upgrade: does this affect us? We use lstchain here and there, so maybe we need to be sure it works as before (e.g. in create_dl3_index_files.py and maybe in io.py, where add_delta_t_key is used; I guess that at lower level, i.e. cleaning and muon analysis, nothing has been really changed, I hope, but we can check)

[YoshikiOhtani]

Thanks @aleberti, it is a good point. I looked into the changes on lstchain and it actually affects our pipeline, at least we need to modify create_dl3_index_files. But this is beyond the purpose of this pull request, so I will get the lstchain-related versions to the original ones.

[YoshikiOhtani]

The environment is created successfully, so I will merge it to the master branch.