Sigma should be double? on ExtendedStatsBucketAggregation

see #1982 and elastic/elasticsearch#17499

Author: russcam

Diff for: src/Nest/Aggregations/Pipeline/ExtendedStatsBucket/ExtendedStatsBucketAggregation.cs

@@ -8,7 +8,7 @@ namespace Nest
 	public interface IExtendedStatsBucketAggregation : IPipelineAggregation
 	{
 		[JsonProperty("sigma")]
-		int? Sigma { get; set; }
+		double? Sigma { get; set; }
 	}
 
 	public class ExtendedStatsBucketAggregation
@@ -20,7 +20,7 @@ public ExtendedStatsBucketAggregation(string name, SingleBucketsPath bucketsPath
 			: base(name, bucketsPath)
 		{ }
 
-		public int? Sigma { get; set; }
+		public double? Sigma { get; set; }
 
 		internal override void WrapInContainer(AggregationContainer c) => c.ExtendedStatsBucket = this;
 	}
@@ -30,9 +30,9 @@ public class ExtendedStatsBucketAggregationDescriptor
 		, IExtendedStatsBucketAggregation
 	{
 
-		int? IExtendedStatsBucketAggregation.Sigma { get; set; }
+		double? IExtendedStatsBucketAggregation.Sigma { get; set; }
 
-		public ExtendedStatsBucketAggregationDescriptor Sigma(int? sigma) => Assign(a => a.Sigma = sigma);
+		public ExtendedStatsBucketAggregationDescriptor Sigma(double? sigma) => Assign(a => a.Sigma = sigma);
 
 	}
 }

Diff for: src/Tests/Aggregations/Pipeline/ExtendedStatsBucket/ExtendedStatsBucketAggregationUsageTests.cs

@@ -38,7 +38,7 @@ public ExtendedStatsBucketAggregationUsageTests(ReadOnlyCluster cluster, Endpoin
 					extended_stats_bucket = new
 					{
 						buckets_path = "projects_started_per_month>commits",
-						sigma = 2
+						sigma = 2.0
 					}
 				}
 			}