fixed RDSInstance#pending_maintenance_actions validate parameter error
fixed RDSInstance#pending_maintenance_actions validate parameter error

aws/aws-sdk-ruby,cjyclaire/aws-sdk-ruby,cjyclaire/aws-sdk-ruby,takeyuweb/aws-sdk-ruby,hamadata/aws-sdk-ruby,takeyuweb/aws-sdk-ruby,aws/aws-sdk-ruby,llooker/aws-sdk-ruby,hamadata/aws-sdk-ruby,llooker/aws-sdk-ruby,cjyclaire/aws-sdk-ruby,takeyuweb/aws-sdk-ruby,hamadata/aws-sdk-ruby,llooker/aws-sdk-ruby,aws/aws-sdk-ruby