chore: move from preview_iam to iam token endpoint

Author: manisha1997

lib/twilio-ruby/http/client_token_manager.rb

@@ -20,7 +20,7 @@ def initialize(grant_type, client_id, client_secret, code = nil, redirect_uri =
       def fetch_access_token
         client = Twilio::REST::Client.new
         token_instance = client.iam.v1.token.create(grant_type: @grant_type,
-                                                            client_id: @client_id, client_secret: @client_secret)
+                                                    client_id: @client_id, client_secret: @client_secret)
         token_instance.access_token
       end
     end

lib/twilio-ruby/http/org_token_manager.rb

@@ -20,7 +20,7 @@ def initialize(grant_type, client_id, client_secret, code = nil, redirect_uri =
       def fetch_access_token
         client = Twilio::REST::Client.new
         token_instance = client.iam.v1.token.create(grant_type: @grant_type,
-                                                            client_id: @client_id, client_secret: @client_secret)
+                                                    client_id: @client_id, client_secret: @client_secret)
         token_instance.access_token
       end
     end