Update ddtrace/span.py

Co-Authored-By: majorgreys <[email protected]>

Author: brettlangdon

ddtrace/span.py

@@ -135,7 +135,7 @@ def set_tag(self, key, value):
             try:
                 self.set_metric(key, float(value))
             except (TypeError, ValueError):
-                log.debug("error setting numeric metric {}:{}".format(key, value))
+                log.debug('error setting numeric metric {}:{}'.format(key, value))
 
             return
         try: