fix selection bug for IE
Merge pull request #121 from teambition/master

fix selection bug for IE
处理插入代码时出现undefined的情况

双击某个地方选中一个单词，点击code，会出现undefined字样。不确定是否是意料中的行为，或者也有可能是前面没处理好导致undefined出现
Merge pull request #122 from TooBug/patch-1

处理插入代码时出现undefined的情况
Merge pull request #3 from sofish/master

merge latest changes in main branch