Any version 2 of ruby should do it.

oubiwann · oubiwann · commit d3361dc26dbb · 2017-02-28T20:19:50.000-06:00
diff --git a/priv/sass/Gemfile b/priv/sass/Gemfile
@@ -1,5 +1,5 @@
 source "http://rubygems.org"
 
-ruby '~> 2.0.0'
+ruby '~> 2'
 
-gem 'sass', '~> 3.4', '>= 3.4.23'
+gem 'sass', '~> 3.4', '>= 3.4.23'
