update ruby version in gemfile and docs

[stefandecimelli]

Description

Updates the ruby version required to run the doc server, in order for the docker container to pick it up. Edit the doc to show this as well.

Addressed Issue

fixes #4247

Additional Details

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[stefandecimelli]

closed due to improper commit signoff