Add missing ; to the end of definition of buffer_t
          #303
        
          
      
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resolve #302
Description
Adds the missing ending
;in the definition ofbuffer_tin02-usability.md.Change List
book/en-us/02-usability.mdReference
说明
添加缺失的结尾
;到02-usability.md中buffer_t的定义。变化箱单
book/en-us/02-usability.md的描述性错误参考文献