Update "generated file" hint to follow go convention. (#161)

Go has a documented[1] convention identifying "generated" files:

> To convey to humans and machine tools that code is generated,
> generated source should have a line that matches the following
> regular expression (in Go syntax):
> ^// Code generated .* DO NOT EDIT\.$

[1]: https://golang.org/pkg/cmd/go/internal/generate/

Author: kadrach

python/rpdk/go/templates/main.go.tple

@@ -1,3 +1,4 @@
+// Code generated by 'cfn generate', changes will be undone by the next invocation. DO NOT EDIT.
 package main
 
 import (
@@ -10,11 +11,6 @@ import (
 	"{{ path }}"
 )
 
-/*
-This file is autogenerated, do not edit;
-changes will be undone by the next 'cfn generate' command.
-*/
-
 // Handler is a container for the CRUDL actions exported by resources
 type Handler struct{}
 

python/rpdk/go/templates/types.go.tple

@@ -1,12 +1,7 @@
+// Code generated by 'cfn generate', changes will be undone by the next invocation. DO NOT EDIT.
+// Updates to this type are made my editing the schema file and executing the 'generate' command.
 package resource
 
-/*
-This file is autogenerated, do not edit;
-changes will be undone by the next 'generate' command.
-
-Updates to this type are made my editing the schema file
-and executing the 'generate' command
-*/
 {% for model_name, properties in models.items() %}
 
 {% if model_name == "ResourceModel" %}