[Bug] rehype-hljs-var fails for hcl snippets

[ptgott]

Given the following MDX page:

---
title: Test page
description: Test page
---

This is a var in an hcl block:

```hcl
provider "teleport" {
  addr        = '<Var name="teleport.example.com:443" />'
  join_method = '<Var name="token-join-method" />'
  join_token  = "terraform_bot"
}

The dev server renders the following:

The rehype-hljs-var plugin replaces Var tags with a placeholder string, applies syntax highlighting with hljs, then replaces the placeholder string with the original Var tags. In this case, the second replacement does not occur. Fix the plugin so it renders Var components correctly in HCL snippets.

[ptgott]

Fixed in #506