[vtkusers] ParaView:Extend webpage error

[David Borland]

The example vtkCellDerivatives.pvsm file at

http://www.paraview.org/Wiki/ParaView:Extend

has an error. The

</ServerManagerConfiguration

line should read

</ServerManagerConfiguration>

It's not much, but causes some confusing errors when trying to add it to 
ParaView.

David