Correcting vtk install condition.
Correcting vtk install condition.

johnnyliu27/openmc,walshjon/openmc,amandalund/openmc,wbinventor/openmc,amandalund/openmc,walshjon/openmc,paulromano/openmc,paulromano/openmc,shikhar413/openmc,smharper/openmc,amandalund/openmc,smharper/openmc,paulromano/openmc,liangjg/openmc,johnnyliu27/openmc,mit-crpg/openmc,shikhar413/openmc,liangjg/openmc,johnnyliu27/openmc,mit-crpg/openmc,shikhar413/openmc,wbinventor/openmc,mit-crpg/openmc,mit-crpg/openmc,shikhar413/openmc,walshjon/openmc,johnnyliu27/openmc,smharper/openmc,liangjg/openmc,amandalund/openmc,liangjg/openmc,paulromano/openmc,wbinventor/openmc,walshjon/openmc,smharper/openmc,wbinventor/openmc