Links with href attributes via hrefBuilder should not have a button role

[mattc-cogapp]

In #211 (related issue: #212), the behaviour of setting a role of button on links with no href attribute was added. However; when using the hrefBuilder prop, any page links will have an href, and should not take on the role of button.

I'm happy to tackle a PR for this, however I just wanted to check the following couple of things:

• Is this a PR you even want?
• What would your expected behaviour be?

Initially, my assumption would be that essentially we want something like this (hastily written pseudo-code), where we only assign the role of button if the hrefBuilder prop isn't defined:

role={typeof this.props.hrefBuilder === 'undefined' ? 'button' : null} 

[MonsieurV]

Hi @mattc-cogapp,

If you provide the PR, I'll merge it. Ok with the solution proposed, no need for more complicated I think (like allowing to define a role by props).