nexus: 3.18.1-01 -> 3.19.1-01

Relevant release notes:

* https://help.sonatype.com/repomanager3/release-notes/2019-release-notes#id-2019ReleaseNotes-RepositoryManager3.19.1
* https://help.sonatype.com/repomanager3/release-notes/2019-release-notes#id-2019ReleaseNotes-RepositoryManager3.19.0

Also added `preferLocalBuild = true;` to prevent builds on remote
machines as this only means elevated network access (tarball is fetched
locally and uploaded to the builder) and the build is fairly trivial.

To fix the startup I had to add the JVM parameter `java.endorsed.dirs`
to ensure that all libraries are loaded properly[1].

[1] https://issues.sonatype.org/browse/NEXUS-21603