Fix bug for headers with bold text

Fixing a bug for headers h1, h2, h3, h4 that have bold text. Currently, extra asterisks are shown in Slack which messes up the formatting. This seems to affect bold tags within header tags when the entire header isn't bolded.

Example:

• Currently <h1>h1 <b>with bold text</b></h1> html is transformed into *h1 *with bold text** and this displays the exact same way in Slack
• With this fix in place, the <h1>h1 <b>with bold text</b></h1> html is transformed into *h1 with bold text* and displays as h1 with bold text in Slack