提交：修改插件配置；

ios/aliyun_face_plugin.podspec

@@ -17,6 +17,7 @@ A new Flutter plugin project.
   s.public_header_files = 'Classes/**/*.h'
   s.dependency 'Flutter'
   s.platform = :ios, '9.0'
+  s.swift_version = '4.0'
 
   # Flutter.framework does not contain a i386 slice.
   s.pod_target_xcconfig = { 'DEFINES_MODULE' => 'YES', 'EXCLUDED_ARCHS[sdk=iphonesimulator*]' => 'i386' }