process_cpu_seconds_total should be scaled from nano's, not milli's

[Jeroen Baekelandt]

In io.prometheus.metrics.instrumentation.jvm.ProcessMetrics, the value returned from callLongGetter("getProcessCpuTime", osBean) is in nanoseconds, but is scaled with Unit.millisToSeconds(processCpuTime)

[Fabian Stäber]

Thanks a lot! Fixed in #882.