Fix a minor typo in debug log message

Author: LotharSee

ddtrace/api.py

@@ -53,7 +53,7 @@ def send_traces(self, traces):
             self._downgrade()
             return self.send_traces(traces)
 
-        log.debug("reported %d spans in %.5fs", len(traces), time.time() - start)
+        log.debug("reported %d traces in %.5fs", len(traces), time.time() - start)
         return response
 
     def send_services(self, services):