Set the swift version and any other build setting of the installed cocoapods;

Podfile

#... Pods defined above

post_install do |installer|
  installer.pods_project.targets.each do |target|
    if ['URITemplate'].include? target.name
      target.build_configurations.each do |config|
        config.build_settings['SWIFT_VERSION'] = '4.0'
      end
    else
        target.build_configurations.each do |config|
            config.build_settings['SWIFT_VERSION'] = '5.0'
        end
    end
  end
end