Update theme name in Gruntfile.js

[felipeelia]

This PR changes the theme name in Gruntfile.js, otherwise theme files won't be affected by grunt sass or grunt watch commands.

Seems to be related to #154.

[Clorith]

It looks like you might have an old version of the directory, I'd recommend doing a pull first.

Also, theme-related stuff is already covered by the gruntfile in the theme directory, we should remove it from the root-gruntfile to avoid unexpected collisions or surprises.

[felipeelia]

Sorry @Clorith. The file isn't that way here? I did a pull first...

And to use theme's Gruntfile we should update it's grunt-sass version, like was done in #197. The actual version didn't work for me (maybe it's too old?).

Sorry if am I not seeing something obvious here.