Add sum_other_doc_count to bucket agg response

Closes #1041

Author: gmarz

src/Nest/Domain/Aggregations/Bucket.cs

@@ -11,6 +11,7 @@ public class Bucket : IAggregation
 	{
 		public IEnumerable<IAggregation> Items { get; set; }
 		public long? DocCountErrorUpperBound { get; set; }
+		public long? SumOtherDocCount { get; set; }
 	}
 
 	public class BucketWithDocCount<TBucketItem> : BucketAggregationBase, IBucketWithCountAggregation

src/Nest/Resolvers/Converters/Aggregations/AggregationConverter.cs

@@ -300,7 +300,13 @@ private IAggregation GetBucketAggregation(JsonReader reader, JsonSerializer seri
 				bucket.DocCountErrorUpperBound = reader.Value as long?;
 				reader.Read();
 			}
-
+			property = reader.Value as string;
+			if (property == "sum_other_doc_count")
+			{
+				reader.Read();
+				bucket.SumOtherDocCount = reader.Value as long?;
+				reader.Read();
+			}
 			var aggregations = new List<IAggregation>();
 			reader.Read();
 			if (reader.TokenType != JsonToken.StartArray)