only set end_time on finish, not start

lib/lightstep/tracer/span.rb

@@ -13,7 +13,6 @@ module LightStep
       child_of_guid: nil,
       trace_guid:,
       start_micros:,
-      end_micros: nil,
       tags: nil
     )
       @tags = Hash(tags)
@@ -23,7 +22,6 @@ module LightStep
       @guid = tracer.generate_guid
       self.operation_name = operation_name
       self.start_micros = start_micros
-      self.end_micros = end_micros
       self.trace_guid = trace_guid
       set_tag(:parent_span_guid, child_of_guid) if !child_of_guid.nil?
     end

lib/lightstep/tracer/tracer.rb

@@ -72,13 +72,9 @@ module LightStep
       @max_flush_period_micros = [DEFAULT_MAX_REPORTING_PERIOD_SECS, secs].min * 1E6
     end
 
-    # ----------------------------------------------------------------------------
-    #  OpenTracing API
-    # ----------------------------------------------------------------------------
-
     # Starts a new span.
     # TODO(ngauthier@gmail.com) inherit SpanContext from references
-    def start_span(operation_name, child_of: nil, start_time: nil, end_time: nil, tags: nil)
+    def start_span(operation_name, child_of: nil, start_time: nil, tags: nil)
       child_of_guid = nil
       trace_guid = nil
       if Span === child_of
@@ -94,7 +90,6 @@ module LightStep
         child_of_guid: child_of_guid,
         trace_guid: trace_guid,
         start_micros: start_time.nil? ? now_micros : micros(start_time),
-        end_micros: end_time.nil? ? nil : micros(end_time),
         tags: tags
       )
     end

spec/lightstep_spec.rb

@@ -80,12 +80,12 @@ describe LightStep do
     span1.finish
     expect(span1.start_micros).to eq(t1_micros)
 
-    span2 = tracer.start_span('test2', end_time: t1)
-    span2.finish
+    span2 = tracer.start_span('test2')
+    span2.finish(end_time: t1)
     expect(span2.end_micros).to eq(t1_micros)
 
-    span3 = tracer.start_span('test3', start_time: t1, end_time: t2)
-    span3.finish
+    span3 = tracer.start_span('test3', start_time: t1)
+    span3.finish(end_time: t2)
     expect(span3.start_micros).to eq(t1_micros)
     expect(span3.end_micros).to eq(t2_micros)
   end