During upgrade, change directory in main process instead of workers.
During upgrade, change directory in main process instead of workers.

This Fixes #468 by making sure the new `cwd` will be used for all the
workers spawned in the future.

matthewd/puma,unleashed/puma,BenV/puma,puma/puma,nathansamson/puma,jbmyid/puma,kyledrake/puma,looker/puma,unleashed/puma,matthewd/puma,eileencodes/puma,ngpestelos/puma,prathamesh-sonpatki/puma,kyledrake/puma,looker/puma,kyledrake/puma,matthewd/puma,prathamesh-sonpatki/puma,jbmyid/puma,costi/puma,nathansamson/puma,wallclockbuilder/puma,looker/puma,ngpestelos/puma,jc00ke/puma,ngpestelos/puma,BenV/puma,zBMNForks/puma,unleashed/puma,costi/puma,arturocadena/puma,zBMNForks/puma,eileencodes/puma,costi/puma,jc00ke/puma,tuvistavie/puma,puma/puma,tuvistavie/puma,tuvistavie/puma,ngpestelos/puma,arturocadena/puma,looker/puma,jc00ke/puma,respire/puma,zBMNForks/puma,wallclockbuilder/puma,BenV/puma,zapnap/puma,respire/puma,zapnap/puma,jc00ke/puma,respire/puma,jbmyid/puma,wallclockbuilder/puma,snow/puma,zapnap/puma,jbmyid/puma,snow/puma,zBMNForks/puma,zapnap/puma,eileencodes/puma,matthewd/puma,wallclockbuilder/puma,nathansamson/puma,snow/puma,puma/puma,prathamesh-sonpatki/puma,respire/puma,puma/puma,costi/puma,tuvistavie/puma,arturocadena/puma,prathamesh-sonpatki/puma,snow/puma,arturocadena/puma,BenV/puma,nathansamson/puma,kyledrake/puma,eileencodes/puma,unleashed/puma