IDEA 首次添加Maven plugins无法下载Could not transfer artifact org.apache.maven.plugins:maven-clean-plugin，pom.xml依赖项无法下载Could not transfer artifact javax.servlet:javax.servlet-api:pom
错误内容：Could not transfer artifact org.apache.maven.plugins:maven-clean-plugin:pom:2.5 from/to alimaven (https://maven.aliyun.com/repository/central): Transfer failed for https://maven.aliyun.com/repository/central/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
最终解决方式（不知道为什么）：
1.设置镜像
2.双击右侧的clean开始了下载，多双击几个之后全部下载完成。