fix json name of DmPermission field

src/Discord.Net.Rest/API/Common/ApplicationCommand.cs

@@ -26,7 +26,7 @@ namespace Discord.API
         public Optional<bool> DefaultPermissions { get; set; }
 
         // V2 Permissions
-        [JsonProperty("dm_permissions")]
+        [JsonProperty("dm_permission")]
         public Optional<bool?> DmPermission { get; set; }
 
         [JsonProperty("default_member_permissions")]

src/Discord.Net.Rest/API/Rest/CreateApplicationCommandParams.cs

@@ -19,7 +19,7 @@ namespace Discord.API.Rest
         [JsonProperty("default_permission")]
         public Optional<bool> DefaultPermission { get; set; }
 
-        [JsonProperty("dm_permissions")]
+        [JsonProperty("dm_permission")]
         public Optional<bool?> DmPermission { get; set; }
 
         [JsonProperty("default_member_permissions")]