PD-18585 fix typo

Author: simonirwin-r7

lib/convection/model/template/resource/aws_elbv2_load_balancer.rb

@@ -18,7 +18,7 @@ class ELBV2LoadBalancer < Resource
           alias security_groups security_group
           property :subnet, 'Subnets', :type => :list
           alias subnets subnet
-          property lb_type, 'Type'
+          property :lb_type, 'Type'
           property :subnet_mappings, 'SubnetMappings', :type => :list
 
           # Append a load_balancer_attribute to load_balancer_attributes