Maven报错，求解答

[hfq03]

刚刚安装maven3
执行命令 mvn help:system

报下面的错误：

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-help-plugin:2.1.1:
system (default-cli) on project standalone-pom: Execution default-cli of goal or
g.apache.maven.plugins:maven-help-plugin:2.1.1:system failed: Plugin org.apache.
maven.plugins:maven-help-plugin:2.1.1 or one of its dependencies could not be re
solved: Failure to find junit:junit:jar:3.8.1 in http://repo.maven.apache.org/ma
ven2 was cached in the local repository, resolution will not be reattempted unti
l the update interval of central has elapsed or updates are forced -> [Help 1]

怎么解决？