Fix relative path in modules/doc/moosedocs.py
Fix relative path in modules/doc/moosedocs.py

(refs #11361)

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