Change SnapshotShardFailure shard_id to int (#4543)

This commit changes the type of property ShardId
on SnapshotShardFailure to int, to match Elasticsearch.

Fixes #4537

Author: russcam

src/Nest/Modules/SnapshotAndRestore/Snapshot/SnapshotShardFailure.cs

@@ -15,7 +15,7 @@ public class SnapshotShardFailure
 		public string Reason { get; set; }
 
 		[DataMember(Name ="shard_id")]
-		public string ShardId { get; set; }
+		public int ShardId { get; set; }
 
 		[DataMember(Name ="status")]
 		public string Status { get; set; }