translate the terminlogy "patch level" as symver.org suggests

zh_CN/chapter03/packages.po

@@ -972,7 +972,7 @@ msgid ""
 "patch level upgrade within a minor release."
 msgstr ""
 "对于那些上网很慢或者流量很贵的用户来说，可以分别下载内核的基线版本和补丁。这"
-"可以节省内核补丁版本 (patch level) 升级时的下载时间和网费。"
+"可以节省内核修订号更新时的下载时间和网费。"
 
 #. type: Content of: <sect1><variablelist><varlistentry><term>
 #: /home/xry111/svn-repos/LFS-BOOK/chapter03/packages.xml:454