Updated nodejs to v16

Testing showed no apparent issues.

To be tagged v5.3.9

thirdparty/terraform-aws-kinesis-firehose-splunk/README.XDR.md

@@ -1,2 +1,2 @@
 Changes:
-
+* variable "nodejs_runtime" default changed from "nodejs12.x" to "nodejs16.x"

thirdparty/terraform-aws-kinesis-firehose-splunk/variables.tf

@@ -18,7 +18,7 @@ variable "hec_token" {
 
 variable "nodejs_runtime" {
   description = "Runtime version of nodejs for Lambda function"
-  default     = "nodejs12.x"
+  default     = "nodejs16.x"
 }
 
 variable "firehose_name" {