Fix doctest, use new error formatting (list instead of string)
Fix doctest, use new error formatting (list instead of string)

funkyfuture/cerberus,pyeve/cerberus,dkellner/cerberus,nicolaiarocci/cerberus,nicolaiarocci/cerberus,funkyfuture/cerberus,pyeve/cerberus,dkellner/cerberus