2.3.0

• Auto-install the right bundler version (#168),
• Test against Ruby 2.4, 2.5, 2.6, 2.7 (#166),
• Allow specifying the path option to bundler (#165),
• Fix acceptance tests under JRuby (#167),
• Make git_source work in nested groups (#160),
• Drop MRI 1.8.7-2.2 support (#158),
• Document all commands in README (#142),
• Allow passing through of the full-index option. (#137),
• Avoid line continuations without parentheses (#138),
• Added RBX to the build matrix (#117),
• Remove suggestion of RubyGems in Rakefiles (#128),
• Update README.md to add appraisal in gemspec instead of Gemfile (#122).