fix broken check box action usage

[mstrYoda]

This pr fixes the issue: #232

Currently the checkbox action is not work well. It breaks the content when you add a checkbox and add new lines.

I add broken example screenshots and fixed one.

Here is the broken one, it is trying to include every content in the html:

Broken on new line:

Fixed version:

[mstrYoda]

Hi @stulip, can you review this one when you available?

[Boluwatife2904]

+1 @stulip . Thank you so much.