Add json properties to difficulty attributes

osu.Game.Rulesets.Osu/Difficulty/OsuDifficultyAttributes.cs

@@ -1,21 +1,41 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using Newtonsoft.Json;
 using osu.Game.Rulesets.Difficulty;
 
 namespace osu.Game.Rulesets.Osu.Difficulty
 {
     public class OsuDifficultyAttributes : DifficultyAttributes
     {
+        [JsonProperty("aim_strain")]
         public double AimStrain { get; set; }
+
+        [JsonProperty("speed_strain")]
         public double SpeedStrain { get; set; }
+
+        [JsonProperty("flashlight_rating")]
         public double FlashlightRating { get; set; }
+
+        [JsonProperty("slider_factor")]
         public double SliderFactor { get; set; }
+
+        [JsonProperty("approach_rate")]
         public double ApproachRate { get; set; }
+
+        [JsonProperty("overall_difficulty")]
         public double OverallDifficulty { get; set; }
+
+        [JsonProperty("drain_rate")]
         public double DrainRate { get; set; }
+
+        [JsonProperty("hit_circle_count")]
         public int HitCircleCount { get; set; }
+
+        [JsonProperty("slider_count")]
         public int SliderCount { get; set; }
+
+        [JsonProperty("spinner_count")]
         public int SpinnerCount { get; set; }
     }
 }