ruby.rb

bundle install
Fetching gem metadata from https://rubygems.org/............
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Fetching nio4r 2.2.0


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      bundle install --path vendor/bundle

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Installing nio4r 2.2.0 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /tmp/bundler20180205-5873-llgyvunio4r-2.2.0/gems/nio4r-2.2.0/ext/nio4r
/usr/bin/ruby2.3 -r ./siteconf20180205-5873-g9pe3o.rb extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in /tmp/bundler20180205-5873-llgyvunio4r-2.2.0/gems/nio4r-2.2.0 for inspection.
Results logged to /tmp/bundler20180205-5873-llgyvunio4r-2.2.0/extensions/x86_64-linux/2.3.0/nio4r-2.2.0/gem_make.out

An error occurred while installing nio4r (2.2.0), and Bundler cannot continue.
Make sure that `gem install nio4r -v '2.2.0'` succeeds before bundling.

In Gemfile:
  rubydns was resolved to 2.0.1, which depends on
    async-dns was resolved to 1.0.0, which depends on
      async-io was resolved to 1.2.0, which depends on
        async was resolved to 1.2.2, which depends on
          nio4r