Catch up to sonatype changes

[rjrjr]

We've moved from oss.sonatype.org to s01.oss.sonatype.org. Need to reconfigure, and update RELEASING.md.

If using Gradle:

repositories {
  mavenCentral()
  maven {
    url 'https://s01.oss.sonatype.org/content/repositories/snapshots/'
  }
}

If using the gradle-maven-publish-plugin plugin, you need a special config:

allprojects {
    plugins.withId("com.vanniktech.maven.publish") {
        mavenPublish {
            sonatypeHost = "S01"
        }
    }
}