Housekeeping Items

[sambostock]

There are a couple things we could to improve the gem:

• Specify a required_ruby_version in gemspec
  This makes it clear to consumers which versions of Ruby we commit to supporting.
  • We only test against Ruby 2.5 and greater, so it seems reasonable that it should be at least >= 2.5
    • However, the Ruby 2.5 EOL date was 2021-03-31, so maybe we should use >= 2.6 and stop testing against 2.5?
• Bump the Rubocop TargetRubyVersion to match the above (it is currently 2.4.4, whose EOL date was 2020-03-31
• Remove Gemfile.lock from .gitignore, as per this post on the Bundler blog
  • Setup Dependabot to keep dependencies up to date.
    • Does Dependabot support our multiple gemfiles?
• Add internal Shopify owners to the gem