Fix docs to say 'childOf' not 'parent'
Fix docs to say 'childOf' not 'parent'

lightstephq/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript