Change GameParty size types to longs. (#955)

src/Discord.Net.Core/Entities/Activities/GameParty.cs

@@ -1,11 +1,11 @@
-namespace Discord
+namespace Discord
 {
     public class GameParty
     {
         internal GameParty() { }
 
         public string Id { get; internal set; }
-        public int Members { get; internal set; }
-        public int Capacity { get; internal set; }
+        public long Members { get; internal set; }
+        public long Capacity { get; internal set; }
     }
-}
+}