Fix reference to node_modules in built package

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/29192

See https://gitlab.slack.com/archives/frontend/p1488973548024005

lib/gitlab/emoji.rb

@@ -31,7 +31,7 @@ module Gitlab
     end
 
     def emoji_unicode_version(name)
-      @emoji_unicode_versions_by_name ||= JSON.parse(File.read(Rails.root.join('node_modules', 'emoji-unicode-version', 'emoji-unicode-version-map.json')))
+      @emoji_unicode_versions_by_name ||= JSON.parse(File.read(Rails.root.join('fixtures', 'emojis', 'emoji-unicode-version-map.json')))
       @emoji_unicode_versions_by_name[name]
     end
 

lib/tasks/gemojione.rake

 namespace :gemojione do
   desc 'Generates Emoji SHA256 digests'
-  task digests: :environment do
+  task digests: ['yarn:check', 'environment'] do
     require 'digest/sha2'
     require 'json'
 
+    # We don't have `node_modules` available in built versions of GitLab
+    FileUtils.cp_r(Rails.root.join('node_modules', 'emoji-unicode-version', 'emoji-unicode-version-map.json'), File.join(Rails.root, 'fixtures', 'emojis'))
+
     dir = Gemojione.images_path
     resultant_emoji_map = {}