Fixed libsass (python) inclusion errors

[goutnet]

Hi,

I am using mdb-ui-kit in a python project (django), and include directly the SASS layer from my main.scss.

As it turns, libsass doesn't like a few lines in the code, so I fixed it and would like to share the update for you.

Mainly:

• optionnal arguments must come after mandatory argument (fixed by providing reasonable defaults)
• rgb function doesn't like the r g b / a notation (fixed by using rgba instead)