Fix NumberPropertyItem parsing issue

Author: KoditkarVedant

Src/Notion.Client/Models/PropertyItems/NumberPropertyItem.cs

@@ -7,6 +7,6 @@ public class NumberPropertyItem : SimplePropertyItem
         public override string Type => "number";
 
         [JsonProperty("number")]
-        public Number Number { get; set; }
+        public double Number { get; set; }
     }
 }