Bumping .NET assembly version number before 6.4.2 release as there were changes

Source commit: f19873147f20fa0773f43425b42401857efebfc7

dotnet/properties/AssemblyInfo.cs

@@ -35,7 +35,7 @@ namespace WinSCP
     {
         public const string UndefinedProductVersion = "9.9.9.9";
 
-        public const string Version = "1.15.0.0";
+        public const string Version = "1.16.0.0";
         public const string ProductVersion = "6.4.2.0";
     }
 }