Fix LongTaskTimer output for LoggingMeterRegistry

[jonatan-ivanov]

Creating and starting a simple LongTaskTimer:

registry.more().longTaskTimer("my.ltt").start();
// wait (1s)
// print

Results in an output like this:

my.ltt{} active=1 milliseconds duration=1s

where the active field should be the number of active tasks, so it should be unit less instead of milliseconds:

my.ltt{} active=1 duration=1s