swift5.0上报警告：substring(to:)' is deprecated: Please use String slicing subscript with a 'partial range upto' opera
解决办法：
let subStr = String(value[..<index]) // = str.substring(to: index) is deprecated
let subStr = String(value[index...]) // = str.substring(from: index) is deprecated
let subStr = String(value[range]) // = str.substring(with: range) is deprecated
