Given a list of service dependencies, how would you determine the order of deployment?
Each dependency is represented as [service, dependency], meaning service requires dependency to be deployed first. Return a valid deployment order containing every service. If multiple services are available, choose the lexicographically smallest service first. Return an empty list if the dependencies contain a cycle.
Implement def deployment_order(dependencies):, where the input and output are lists of strings.
def deployment_order(dependencies):