Certain code tag content breaks AMP output

Issue Summary

Adding '$example$' to the markdown truncates the AMP output before the second $ causing broken browser rendering through missing closing tags.

To Reproduce

1. Create a new post and set the content to:

Testing

`'$example$'` asdf

123

1. Publish the post and open the AMP version on the blog front-end. Note the broken display and missing content after '$example.

The HTML output is clearly malformed. the trailing $' is removed and the rest of the helper output is added to the bottom of the post with the final section duplicated:

This results in the browser injecting lots of extra <code></code> tags to try and deal with the malformed HTML.

Removing the SafeString call so that handlebars outputs the raw string appears to show that there’s a nested async helper issue:

<div class="kg-card-markdown">
  <p>Testing</p>
  <p>
    <code>'$example__aSyNcId_<_ZziCMbqm__#x27;</code>
    asdf
  </p>
  <p>123</p>
</div>

Narrowing the troublesome content down it appears to be caused by a trailing $ or $' in any element. This can be demonstrated with simply putting $ as the only markdown content in a post.

Technical details:

• Ghost Version: 1.24.7
• Node Version: 8.10.0
• Browser/OS: n/a
• Database: SQLite

[jtwebman]

Opened a PR. https://github.com/barc/express-hbs/pull/149

Once it is merged and published in a new version we can open a PR to update the version in this repo.

[jtwebman]

Still waiting for the permissions to publish the merge and then we can make sure this fixes this issue by testing out the new version here.