Stop require of i18n-tasks (#2992)

Gemfile

@@ -61,7 +61,7 @@ gem 'webpacker', '~> 1.2'
 group :development, :test do
   gem 'fabrication', '~> 2.16'
   gem 'fuubar', '~> 2.2'
-  gem 'i18n-tasks', '~> 0.9'
+  gem 'i18n-tasks', '~> 0.9', require: false
   gem 'pry-rails', '~> 0.3'
   gem 'rspec-rails', '~> 3.6'
 end