Add trace_guid to thrift reporting structure

lib/lightstep/tracer/client_span.rb

@@ -106,6 +106,7 @@ class ClientSpan
 
     rec = SpanRecord.new(runtime_guid: @tracer.guid.to_s,
                          span_guid: @guid.to_s,
+                         trace_guid: @trace_guid.to_s,
                          span_name: @operation.to_s,
                          attributes: attributes,
                          oldest_micros: @start_micros.to_i,

spec/lightstep_spec.rb

@@ -91,6 +91,11 @@ describe LightStep do
     children2.each(&:finish)
     parent1.finish
     parent2.finish
+
+    (children1.concat children2).each do |child|
+      thrift_data = child.to_thrift
+      expect(thrift_data.trace_guid).to eq(child.trace_guid)
+    end
   end
 
   it 'should handle all valid payloads types' do