fix(ci): fallback in case of non-existing page

Author: Haroenv

_layouts/pages/install-ci.html

@@ -8,13 +8,30 @@
 
 {{i18n.ci_intro}}
 
-{% capture travis    %}{% include_relative _ci/travis.md    %}{% endcapture %}
-{% capture semaphore %}{% include_relative _ci/semaphore.md %}{% endcapture %}
-{% capture appveyor  %}{% include_relative _ci/appveyor.md  %}{% endcapture %}
-{% capture circle    %}{% include_relative _ci/circle.md    %}{% endcapture %}
-{% capture codeship  %}{% include_relative _ci/codeship.md  %}{% endcapture %}
-{% capture solano    %}{% include_relative _ci/solano.md    %}{% endcapture %}
-{% capture gitlab    %}{% include_relative _ci/gitlab.md    %}{% endcapture %}
+{% capture travis %}
+  {% include_relative _ci/travis.md %}
+{% endcapture %}
+{% capture semaphore %}
+  {% include_relative _ci/semaphore.md %}
+{% endcapture %}
+{% capture appveyor %}
+  {% include_relative _ci/appveyor.md %}
+{% endcapture %}
+{% capture circle %}
+  {% include_relative _ci/circle.md %}
+{% endcapture %}
+{% capture codeship %}
+  {% include_relative _ci/codeship.md %}
+{% endcapture %}
+{% capture solano %}
+  {% include_relative _ci/solano.md %}
+{% endcapture %}
+{% capture gitlab %}
+  {% capture exists %}{% file_exists _ci/gitlab.md %}{% endcapture %}
+  {% if exists == "true" %}
+    {% include_relative _ci/gitlab.md %}
+  {% endif %}
+{% endcapture %}
 
 
 <div class="tabs">

_plugins/file_exists.rb

@@ -0,0 +1,24 @@
+# source: https://github.com/michaelx/jekyll_file_exists/blob/dd363223754836a640de81ddab68fd95cebe7791/file_exists.rb
+module Jekyll
+  class FileExistsTag < Liquid::Tag
+
+      def initialize(tag_name, path, tokens)
+          super
+          @path = path
+      end
+
+      def render(context)
+          # Pipe parameter through Liquid to make additional replacements possible
+          url = Liquid::Template.parse(@path).render context
+
+          # Adds the site source, so that it also works with a custom one
+          site_source = context.registers[:site].config['source']
+          file_path = site_source + '/' + url
+
+          # Check if file exists (returns true or false)
+          "#{File.exist?(file_path.strip!)}"
+      end
+  end
+end
+
+Liquid::Template.register_tag('file_exists', Jekyll::FileExistsTag)