Fix VectorPostprocessorName options in peacock parameter editor.
Fix VectorPostprocessorName options in peacock parameter editor.

It could happen that it would look for VectorPostprocessors
in PostProcessors/* rather than VectorPostprocessors/*

closes #11273

jessecarterMOOSE/moose,SudiptaBiswas/moose,YaqiWang/moose,harterj/moose,bwspenc/moose,andrsd/moose,harterj/moose,idaholab/moose,dschwen/moose,jessecarterMOOSE/moose,idaholab/moose,laagesen/moose,harterj/moose,idaholab/moose,harterj/moose,permcody/moose,idaholab/moose,sapitts/moose,milljm/moose,dschwen/moose,sapitts/moose,SudiptaBiswas/moose,sapitts/moose,jessecarterMOOSE/moose,dschwen/moose,bwspenc/moose,nuclear-wizard/moose,sapitts/moose,harterj/moose,SudiptaBiswas/moose,permcody/moose,milljm/moose,andrsd/moose,jessecarterMOOSE/moose,laagesen/moose,bwspenc/moose,bwspenc/moose,nuclear-wizard/moose,SudiptaBiswas/moose,lindsayad/moose,permcody/moose,sapitts/moose,idaholab/moose,YaqiWang/moose,andrsd/moose,andrsd/moose,permcody/moose,laagesen/moose,milljm/moose,laagesen/moose,YaqiWang/moose,nuclear-wizard/moose,bwspenc/moose,lindsayad/moose,andrsd/moose,dschwen/moose,lindsayad/moose,lindsayad/moose,YaqiWang/moose,jessecarterMOOSE/moose,dschwen/moose,nuclear-wizard/moose,laagesen/moose,SudiptaBiswas/moose,milljm/moose,lindsayad/moose,milljm/moose