update gemfile

Gemfile

@@ -5,7 +5,7 @@ git_source(:github) do |repo_name|
   "https://github.com/#{repo_name}.git"
 end
 
-ruby '2.4.2'
+ruby '2.6.3'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 5.1.4'