You’ll need to install bundler 1.2.x or above to use the ruby keyword and bundler 1.13.x or above to use a Ruby version specifier. You can use the ruby keyword in your app’s Gemfile to specify a specific version of Ruby. source "https://rubygems.org" ruby "2.5.1" # ... Heroku recommends you run the latest Ruby version your app can handle. Ruby 2.5.1 might not be the latest Ruby version, and is her
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