makefile: fix typo to path of create-staging-env script
makefile: fix typo to path of create-staging-env script

heartsucker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop