Make App::_loadVendor() static.
Make App::_loadVendor() static.

Fixes strict warnings.
Fixes #2137

CVO-Technologies/cakephp,ADmad/cakephp,ndm2/cakephp,erikfig/cakephp,Balachan27/cakephp,CakeDC/cakephp,burriko/cakephp,jjj117/cakephp,et304383/passbolt_api,ADmad/cakephp,justinyost/cakephp,tenkoma/cakephp,khoimt/cakephp-study,nrother/cakephp,cakephp/cakephp,elboletaire/cakephp,davidyell/cakephp,dkarvounaris/cakephp,et304383/passbolt_api,ionas/cakephp,et304383/passbolt_api,eboominathan/cakephp,tenkoma/cakephp,dakota/cakephp,jeffblack360/cakephp,jeffblack360/cakephp,bravo-kernel/cakephp,Balachan27/cakephp,eboominathan/cakephp,ADmad/cakephp,burriko/cakephp,davidyell/cakephp,elboletaire/cakephp,elboletaire/cakephp,nrother/cakephp,web-player/cakephp,garethellis36/cakephp,tenkoma/cakephp,petteyg/cakephp,ndm2/cakephp,yinhe007/cakephp,timhoeppner/cakephp,dakota/cakephp,dakota/cakephp,tgr0ss/cakephp,HavokInspiration/cakephp,HavokInspiration/cakephp,web-player/cakephp,adopico/cakephp,eboominathan/cakephp,tisu2tisu/cakephp,jjj117/cakephp,mvdriel/cakephp,berrygoudswaard/cakephp,petteyg/cakephp,HavokInspiration/cakephp,Phillaf/cakephp,jeffblack360/cakephp,eryw/cakephp,kumamidori/cakephp,CVO-Technologies/cakephp,kumamidori/cakephp,berrygoudswaard/cakephp,garethellis36/cakephp,davidyell/cakephp,ionas/cakephp,dkarvounaris/cakephp,garethellis36/cakephp,jerems02/cakephp,mvdriel/cakephp,Balachan27/cakephp,tgr0ss/cakephp,akintoey/cakephp,cakephp/cakephp,CVO-Technologies/cakephp,ADmad/cakephp,nrother/cakephp,bravo-kernel/cakephp,justinyost/cakephp,adopico/cakephp,khoimt/cakephp-study,thinkingmedia/cakephp,dakota/cakephp,ionas/cakephp,timhoeppner/cakephp,mvdriel/cakephp,cakephp-fr/cakephp,adopico/cakephp,jerems02/cakephp,michaelze/cakephp,justinyost/cakephp,Phillaf/cakephp,Phillaf/cakephp,gmponos/cakephp,et304383/passbolt_api,thinkingmedia/cakephp,et304383/passbolt_api,gmponos/cakephp,erikfig/cakephp,ndm2/cakephp,cakephp-fr/cakephp,cakephp-fr/cakephp,CakeDC/cakephp,jerems02/cakephp,yinhe007/cakephp,thinkingmedia/cakephp,eryw/cakephp,gmponos/cakephp,mvdriel/cakephp,kumamidori/cakephp,bravo-kernel/cakephp,berrygoudswaard/cakephp,burriko/cakephp,cakephp/cakephp,tenkoma/cakephp,khoimt/cakephp-study,jjj117/cakephp,erikfig/cakephp,eryw/cakephp,ndm2/cakephp,petteyg/cakephp,pbaire/cakephp,michaelze/cakephp,garethellis36/cakephp,CakeDC/cakephp,pbaire/cakephp,yinhe007/cakephp,pbaire/cakephp,tisu2tisu/cakephp,akintoey/cakephp,dkarvounaris/cakephp,cakephp/cakephp,tisu2tisu/cakephp,web-player/cakephp,CakeDC/cakephp,akintoey/cakephp,petteyg/cakephp,timhoeppner/cakephp,tgr0ss/cakephp,michaelze/cakephp