How to disable canvas fingerprinting in RoR

I have Rails 3 and Rails 4 applications.

Since I installed a Safari extension (JSBlocker) I get an alert saying that my websites may be using canvas fingerprinting to track me.

1. Is it true ?

2. How to disable it, or prevent JSBlocker to believe there is a problem (Must be server side fix).

Here is an extract of my Gemfile in case it could come from a gem:

gem 'devise'
gem 'rails_admin'
gem 'twitter-bootstrap-rails'
gem 'coffee-rails', '~> 4.1.0'
gem 'uglifier', '>= 1.3.0'
gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder', '~> 2.0'