Fixed weird bib btn behavior (alshedivat#1776)

Fixes alshedivat#1774 by reverting mdb usage to cdn. Weirdly enough, when using
from local file it triggers a ripple effect when using `btn` class. It
states in the [official
docs](https://mdbootstrap.com/docs/standard/methods/ripple/) that:

> By default, ripple is added to every button (via .btn class)

Using [this
solution](https://mdbootstrap.com/support/standard/disable-waves-ripple-effect/)
only make this flicking happens faster. Also this does seem to be [an
issue](https://mdbootstrap.com/support/standard/how-to-disable-ripple-effect/)
still in the [latest
version](mdbootstrap/mdb-ui-kit#1505) (even
though we are using an older one).

Signed-off-by: George Araujo <[email protected]>