grunt usemin fix on css assets

gistfile1.txt

I use sass and only I added image dist path to assetsDirs array.
usemin image css path works like so:

usemin: {
    options: {
        assetsDirs: ['<%= yeoman.dist %>', '<%= yeoman.dist %>/images']
    },
    html: ['<%= yeoman.dist %>/{,*/}*.html'],
    css: ['<%= yeoman.dist %>/styles/{,*/}*.css']
},