这个错误是将work offline打勾引起的。
这个是离线工作模式，相当于断网，远程的jar会拉不下来。
[ERROR] Plugin org.apache.maven.plugins:maven-clean-plugin:2.5 or one of its dependencies could not be resolved: Cannot access nexus-aliyun (http://maven.aliyun.com/nexus/content/groups/public) in off
原文：https://www.cnblogs.com/yang101/p/11306285.html
