[nit] Do not use String, instead use str
[nit] Do not use String, instead use str

Rust Best Practice: When we do not need to manipulate the String we
should always prefer to use str instead since it involves a memory
allocation.

Signed-off-by: Salim Afiune <2b0aff3923bd0ab6bbf45ffb37e57dcea8e1b0b8@chef.io>

chef/delivery-cli,chef/delivery-cli,chef/delivery-cli