change span attribute name to match implementations in other langs

Author: marcdel

examples/roll_dice/README.md

@@ -62,7 +62,7 @@ defmodule DiceGameWeb.DiceController do
     Tracer.with_span("roll_dice") do
       roll = Enum.random(1..6)
 
-      Tracer.set_attribute(:roll, roll)
+      Tracer.set_attribute("roll.value", roll)
 
       to_string(roll)
     end

examples/roll_dice/lib/roll_dice_web/controllers/dice_controller.ex

@@ -7,10 +7,10 @@ defmodule RollDiceWeb.DiceController do
   end
 
   defp roll_dice do
-    Tracer.with_span("roll_dice") do
+    Tracer.with_span "roll_dice" do
       roll = Enum.random(1..6)
 
-      Tracer.set_attribute(:roll, roll)
+      Tracer.set_attribute("roll.value", roll)
 
       to_string(roll)
     end