Invalid HTML within Text Block with Markdown enabled breaks the builder

[alexc-harrap]

Seems there is a bug with the Markdown option in the Text Block where it will fatally break the builder if it tries to render invalid html.

Steps to reproduce:

Visit the demo playground:
https://usewaypoint.github.io/email-builder-js/#

Add new Text Block

Wrap text in <a> tags and enable Markdown

Now try add a href to the <a> tag. The builder will break once you type "href"

[alexc-harrap]

I realise the Markdown uses GitHub style markdown which may be the issue here. This was not apparent from the ReadMe or within the builder UI itself how the Markdown feature works. (I found out though one of the past issues #103)