Be able to convert documents that have embedded terraform interpolations that break JSON parsing

[flosell]

(triggered by #13)

When writing policy JSONs inline as heredoc, one often includes terraform interpolations for certain values, e.g.

locals {
  path_elements = ["foo","bar"]
}

resource "aws_iam_policy" "policy" {
  name        = "test_policy"
  path        = "/"
  description = "My test policy"

  policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "s3:Get*"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:s3:::foo/${join("/",local.path_elements)}"
    }
  ]
}
EOF
}

In this example, the extra quotes inside the interpolation make this invalid JSON, we can't parse it.

[flosell]

Fix released in v1.6.0