Issue with colons inside bold tags #3938

Marked version: 4.3 (But seemingly still happens on the latest version too)

Describe the bug
When the copy between bold tags ends in a colon and there is no trailing space after, the bold tags aren't respected, and asterisks are rendered as characters.

To Reproduce
Use the following markdown: **foo:**bar within marked. See below how it looks in the demo:

Expected behavior
Daring Fireball's Markdown render's as I would expect: