Allow new aws api-gateway integration types

The added types are 'AWS_PROXY' for integrating with lambdas and
'HTTP_PROXY' for integrating via http.

See http://docs.aws.amazon.com/apigateway/api-reference/resource/integration/

builtin/providers/aws/resource_aws_api_gateway_integration.go

@@ -45,9 +45,9 @@ func resourceAwsApiGatewayIntegration() *schema.Resource {
 				Required: true,
 				ValidateFunc: func(v interface{}, k string) (ws []string, errors []error) {
 					value := v.(string)
-					if value != "MOCK" && value != "AWS" && value != "HTTP" {
+					if value != "MOCK" && value != "AWS" && value != "HTTP" && value != "AWS_PROXY" && value != "HTTP_PROXY" {
 						errors = append(errors, fmt.Errorf(
-							"%q must be one of 'AWS', 'MOCK', 'HTTP'", k))
+							"%q must be one of 'AWS', 'MOCK', 'HTTP', 'AWS_PROXY', 'HTTP_PROXY'", k))
 					}
 					return
 				},