The autoprefixer-rails gem is outdated, leading to some annoying deprecation messages such as:
DEPRECATION WARNING: You are using the a deprecated processor interface #<Proc:0x0000000c9a3f60@/home/tbrisker/.rvm/gems/ruby-2.0.0-p648@foreman_gemset/gems/autoprefixer-rails-5.2.1.3/lib/autoprefixer-rails/sprockets.rb:25>.
Newer versions also remove default support for legacy browsers we don't support anyways (IE <10).