Add symbolic link for yarnpkg (#7894)

bin/yarn

@@ -2,7 +2,7 @@
 APP_ROOT = File.expand_path('..', __dir__)
 Dir.chdir(APP_ROOT) do
   begin
-    exec "yarnpkg #{ARGV.join(' ')}" unless Dir.exist?('node_modules')
+    exec "yarnpkg", *ARGV
   rescue Errno::ENOENT
     $stderr.puts "Yarn executable was not detected in the system."
     $stderr.puts "Download Yarn at https://yarnpkg.com/en/docs/install"