Update package grunt-less deprecated for the new grunt-contrib-less

as suggested in the README
https://github.com/jharding/grunt-less/blob/master/README.md#grunt-less-deprecated
Add a strokeColor options to the Donut class

to be able to present the donut over another background than a white
one.
Merge branch 'master' of https://github.com/peteralaoui/morris.js into peteralaoui-master

Conflicts:
	morris.min.js
Rename strokeColor -> backgroundColor.