How to create index on single property using neo4j ruby

I am trying to create index on ActiveNode properties. when i tried with the code which is specified below , index is creating but it is throwing some warning like "The constraint option is no longer supported (Defined on Neo4j for permalink)" . How to create index on property without warning and error on nodes ?

class Neo4j
  include Neo4j::ActiveNode
  property :permalink, type: String, index: :exact 
end

And whenever i create a active node it should be automatically created after node creation , i am not appreciating functions with queries . I am using "neo4j-core" gem on ruby on rails and version , edition is below:

{
    "edition": "community",
    "version": "3.4.1"
}