Bumping .NET assembly version number before 6.2.2 release as there were changes

Source commit: 9f1c38db4287f6be86c4af919db199367b78b697

dotnet/properties/AssemblyInfo.cs

@@ -35,7 +35,7 @@ namespace WinSCP
     {
         public const string UndefinedProductVersion = "9.9.9.9";
 
-        public const string Version = "1.14.0.0";
+        public const string Version = "1.15.0.0";
         public const string ProductVersion = "6.2.2.0";
     }
 }