Update Ruby version (and Gemfile.lock dependencies) #253
Description
Ruby 3.0.0 was [released|https://www.ruby-lang.org/en/news/2020/12/25/ruby-3-0-0-released/] in December 2020, but our {{.tool-versions}} still specifies {{2.x}}. Additionally, a few of the dependencies in {{Gemfile.lock}} are outdated and do not support Ruby 3.0.0.