CocoaPods 给每个库单独指定 Swift 版本

    post_install do |installer|

        installer.pods_project.targets.each do |target|

            if ['Macaw'].include? target.name

                target.build_configurations.each do |config|

                    config.build_settings['SWIFT_VERSION'] = '4.2'

                end

            end

        end

    end