Fix anchor tag with .btn class in alert

[amaury-hanser]

Questions	Answers
Description?	When one uses an anchor tag with the class .btn in an alert, the button will be underlined and the color won't be the one from the class .btn.
Type?	bug fix
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes #157
How to test?	<div class="alert alert-info" role="alert"> <p class="alert-text"> This is a info alert with <a href="#">an example link</a>. Click me to delete </p><div> <a href="//google.com" class="btn btn-secondary"> I'm an a tag </a> </div></div>
Possible impacts?	Don't see any

[Progi1984]

Thanks @amaury-hanser & @sarahdib