Andorra missing its 2-character country code

[VizualAbstract]

It looks like in the recent update (thank you so much!) Andorra was missing its 2-digit country code.

This PR aims to restore that: #33

[ubaldop]

Hi @VizualAbstract thanks for proposing this change. Actually because of #27 I had to do a workaround for Andorra flag.
As you may notice here you can still use ad when declaring the flag, but on component side it is translated to f-andorra CSS class.

[ubaldop]

However I leave your proposal still opened here because instead of restoring "f-ad" it could be better of get rid of "f-andorra" CSS class leaving only "f-and" instead.
So, referring to this, it could become:

country = (country === 'ad') ? 'and' : country

would you mind to align your PR with this improvement?

Doing so could make the component slightly lighter.