在maven install的时候一直报这个错误：
Cannot access nexus (http://maven.enncloud.cn/content/groups/public) in offline mode and the artifact org.springframework.boot:spring-boot-starter-parent:pom:2.0.1.RELEASE............. has not been downloaded from it before.
查找资料发现是,maven默认配置 work offline, 去掉勾选： 
