DockerHub build fails on the master branch

[oleg-nenashev]

See https://cloud.docker.com/u/librecores/repository/registry-1.docker.io/librecores/librecores-ci-dev/builds/b0f6dd1c-5cda-43ff-bace-77a3743ce7ee .

Jun 17, 2019 6:46:39 AM io.jenkins.tools.warpackager.lib.util.MavenHelper listDependenciesFromPom
INFO: Listing dependencies from POM file: pom.xml
[INFO] Scanning for projects...
[WARNING] The POM for org.jenkins-ci.tools:maven-hpi-plugin:jar:3.5 is missing, no dependency i
nformation available
[WARNING] Failed to build parent project for org.librecores.librecores-ci:librecores-ci:pom:1.0-SNAPSH
OT
[I
N

Exception in thread "main" java.io.IOException: Invalid update center url : http://updates.jenkins.io/update-center.json

Maybe just a network glitch on the DockerHub build machine, needs investigation