Update Rails 3.1 to Rails 3.2

In Gemfile, change following versions of assets and rails

gem 'rails', '3.2.0'

group :assets do
  gem 'sass-rails', "  ~> 3.2.3"
  gem 'coffee-rails', "~> 3.2.1"
  gem 'uglifier', '>= 1.0.3'
end

Run 'bundle update'