Add configuration for autoprefixer-rails
Add configuration for autoprefixer-rails

Following #314
mattbeedle/jekyll-assets,jekyll-assets/jekyll-assets,jekyll-assets/jekyll-assets,mattbeedle/jekyll-assets,jekyll/jekyll-assets,jekyll/jekyll-assets,mattbeedle/jekyll-assets,jeremy/jekyll-assets,jekyll/jekyll-assets,jeremy/jekyll-assets,jekyll/jekyll-assets,jekyll-assets/jekyll-assets,jeremy/jekyll-assets,mattbeedle/jekyll-assets,jeremy/jekyll-assets