Fix namespace-directory mismatch (#403)

Author: AlekseyMartynov

net/DevExtreme.AspNet.Data/RemoteGrouping/RemoteAvgAggregator.cs

@@ -1,9 +1,10 @@
-using DevExtreme.AspNet.Data.Helpers;
+using DevExtreme.AspNet.Data.Aggregation;
+using DevExtreme.AspNet.Data.Helpers;
 using DevExtreme.AspNet.Data.Types;
 using System;
 using System.Linq;
 
-namespace DevExtreme.AspNet.Data.Aggregation {
+namespace DevExtreme.AspNet.Data.RemoteGrouping {
 
     class RemoteAvgAggregator<T> : Aggregator<T> {
         Aggregator<T> _countAggregator;