Fix fetch (#5) (#202)
Fix fetch (#5) (#202)

* fix request headers stuff wip

* refactor
lightstephq/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript,lightstephq/lightstep-tracer-javascript,lightstep/lightstep-tracer-javascript