title: How to make Terraform archive_file resource pick up changes to source files?
body: <p>Using TF 0.7.2 on a Win 10 machine.</p>
  
  <p>I'm trying to set up an edit/upload cycle for development of my lambda functions in AWS, using the new "archive_file" resource introduced in TF 0.7.1</p>
  
  <p>My configuration looks like this:</p>
  
  <pre><code>resource "archive_file" "cloudwatch-sumo-lambda-archive" {
    source_file = "${var.lambda_src_dir}/cloudwatch/cloudwatchSumologic.js"
    output_path = "${var.lambda_gen_dir}/cloudwatchSumologic.zip"
    type = "zip"
  }
  
  resource "aws_lambda_function" "cloudwatch-sumo-lambda" {
    function_name = "cloudwatch-sumo-lambda"
    description = "managed by source project"
    filename = "${archive_file.cloudwatch-sumo-lambda-archive.output_path}"
    source_code_hash = "${archive_file.cloudwatch-sumo-lambda-archive.output_sha}"
    handler = "cloudwatchSumologic.handler"
  
    ...
  }
  </code></pre>
  
  <p>This works the first time I run it - TF creates the lambda zip file, uploads it and creates the lambda in AWS.
  The problem comes with updating the lambda.</p>
  
  <p>If I edit the cloudwatchSumologic.js file in the above example, TF doesn't appear to know that the source file has changed - it doesn't add the new file to the zip and doesn't upload the new lambda code to AWS.</p>
  
  <p>Am I doing something wrong in my configuration, or is the archive_file resource not meant to be used in this way?</p>