reduce VTK's version number

The work that we expected that would have justified the major
number bump has been delayed. Therefore, we are going back to 8.2
for the next release.

CMake/vtkVersion.cmake

 # VTK version number components.
-set(VTK_MAJOR_VERSION 9)
-set(VTK_MINOR_VERSION 0)
+set(VTK_MAJOR_VERSION 8)
+set(VTK_MINOR_VERSION 2)
 set(VTK_BUILD_VERSION 0)