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工作认领：米尔、导演
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Update 19_Nested_Types.md

翻译初成
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修改进度
Merge https://github.com/tarobjtu/The-Swift-Programming-Language into tarobjtu-master

Conflicts:
	README.md
Merge branch 'master' of https://github.com/trans4fun/The-Swift-Programming-Language