'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range upto'

swift3 消除警告'substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range upto'  Swift3廢除了subString(from\to\with:)字符串截取方法。 而截取方法改成了： let newStr = String(str[..<index]) // =

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