fix(Makefile): add flake8 to bootstrap
fix(Makefile): add flake8 to bootstrap

flake8 support was recently added, but the bootstrap didn't check or
install it.

adamreese/helm,sparkprime/helm,flynnduism/helm,michelleN/deployment-manager,qwangrepos/helm,adamreese/deployment-manager,helm/helm,helm/helm,rbwsam/helm,FengyunPan/helm,adamreese/deployment-manager,yan234280533/helm,kdada/helm,sparkprime/helm,fibonacci1729/helm,eicnix/helm,migmartri/helm,SlickNik/helm,bradj/helm,technosophos/deployment-manager,qwangrepos/helm,sushilkm/helm,fibonacci1729/helm,sparkprime/helm,FengyunPan/helm,jackgr/helm,jackgr/helm,iamzhout/helm,michelleN/deployment-manager,sparkprime/helm,technosophos/k8s-helm,jascott1/helm,SlickNik/helm,thomastaylor312/helm,adamreese/helm,rbwsam/helm,bacongobbler/helm,sparkprime/helm,eicnix/helm,adamreese/deployment-manager,sushilkm/helm,appscode/helm,jackgr/helm,jackgr/helm,kdada/helm,vaikas-google/deployment-manager,jascott1/helm,technosophos/k8s-helm,technosophos/deployment-manager,flynnduism/helm,thomastaylor312/helm,adamreese/deployment-manager,technosophos/deployment-manager,michelleN/deployment-manager,michelleN/deployment-manager,iamzhout/helm,technosophos/deployment-manager,vaikas-google/deployment-manager,migmartri/helm,yan234280533/helm,technosophos/deployment-manager,adamreese/deployment-manager,appscode/helm,bacongobbler/helm,bradj/helm,jackgr/helm