Change statistic_type of HealthyHostCount and UnHealthyHostCount

Hi

Change statistic_type of HealthyHostCount and UnHealthyHostCount.
Recommended HealthyHostCount and UnHealthyHostCount is [written](http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/US_MonitoringLoadBalancerWithCW.html) as Average.

Please confirm.
Thank you.