Try this. This will navigate to the link on click.
<button onclick="window.location.href='http://www.stackoverflow.com'">click me</button>
Why you don't use <a type="button" href=""></a>
Or if you really want a button, so <button onclick="window.location.href=""></button>
I think this will solve your problem
<a href="http://www.stackoverflow.com/">
<button>click me</button>
</a>
href attribute can not be used on button tag , if you want button like appearance for your a tag you can use add style to your a tag and make it look like button , add bootstrap reference then add button class to your anchor tag. Custom Bootstrap Button , but if you still want to use button tag then adding onclick event is better option