change css output style in Gruntfile.js
change css output style in Gruntfile.js

Changes from @codenameEli that did not merge in smoothly therefore
recreated in this commit.

In Gruntfile.js settings for grunt-sass (which has replaced
grunt-contrib-sass)
option 'style' becomes 'outputStyle'
and outputStyle value 'normal' becomes 'nested'

Closes #18

bryanwillis/bootstrap-genesis,salcode/bootstrap-genesis,salcode/bootstrap-genesis,bryanwillis/bootstrap-genesis,bryanwillis/bootstrap-genesis,michaelcarwile/bootstrap-genesis,michaelcarwile/bootstrap-genesis,salcode/bootstrap-genesis,michaelcarwile/bootstrap-genesis