Updates Readme: Removes ruby version section

The Supported Ruby Version section has the ruby version used, which is
redundant to
https://github.com/codeforamerica/ohana-web-search#stack-overview. It
also provides advice on being a maintainer, but this should appear in
the contribution guidelines if it’s important to mention.
Merge pull request #639 from codeforamerica/remove-readme-ruby-section

Updates Readme: Removes ruby version section