具体错误原因：

Failed to execute goal on project sakai-citations-api: Could not resolve dependencies for project org.sakaiproject:sakai-citations-api:jar:11-SNAPSHOT: Failed to collect dependencies at OKI:OkiOSID:jar:2.0: Failed to read artifact descriptor for OKI:OkiOSID:jar:2.0: Could not transfer artifact OKI:OkiOSID:pom:2.0 from/to opencast-mirror (http://nexus.opencast.org:8081/nexus/content/groups/public): nexus.opencast.org: unknown error: Unknown host nexus.opencast.org: unknown error -> [Help 1]

解决方法：

通常是由于国内网络的原因，使用VPN代理重新mvn install即可

链接：