export SpanContext (#230)
export SpanContext (#230)

Fixes #229
lightstep/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript