Fix RuboCop offenses

- Add rubygems_mfa_required metadata to gemspec
- Fix line endings in Gemfile (CRLF to LF)

Author: mike927

rspec-json_api.gemspec

@@ -16,6 +16,7 @@ Gem::Specification.new do |spec|
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = "https://github.com/nomtek/rspec-json_api"
   spec.metadata["changelog_uri"] = "https://github.com/nomtek/rspec-json_api/blob/master/CHANGELOG.md"
+  spec.metadata["rubygems_mfa_required"] = "true"
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.