The following artifacts could not be resolved: org.eclipse.tycho.extras:tycho-buildtimestamp-egit:jar:0.17.0-SNAPSHOT, org.eclipse.tycho.extras:tycho-sourceref-egit:jar:0.17.0-SNAPSHOT: Could not find artifact org.eclipse.tycho.extras:tycho-buildtimestamp-egit:jar:0.17.0-SNAPSHOT in tycho (https://oss.sonatype.org/content/groups/public/) -> [Help 1]