How to install charlock_holmes dependency libicu-dev on Heroku

I'm using the ruby gem charlock_holmes in a Rails 4 app to detect the character encodings of CSV's that I'm parsing so that CSV.foreach doesn't throw an error. However, when I try to push to heroku (with gem 'charlock_holmes' in the Gemfile) I get the following error: Installing charlock_holmes (0.6.9.4) Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension. /tmp/build_e

[syonx]

Benjie氏の回答が有用だった。加えて Ruby 1.9.3 じゃないとダメみたい。