Update yarn files for rails 6

Also allow `yarnpkg` binary for `bin/yarn`

bin/setup

@@ -17,6 +17,9 @@ FileUtils.chdir APP_ROOT do
   system! 'gem install bundler --conservative'
   system('bundle check') || system!('bundle install')
 
+  # Install JavaScript dependencies
+  system! 'bin/yarn'
+
   # puts "\n== Copying sample files =="
   # unless File.exist?('config/database.yml')
   #   FileUtils.cp 'config/database.yml.sample', 'config/database.yml'

bin/yarn

@@ -1,9 +1,15 @@
 #!/usr/bin/env ruby
 APP_ROOT = File.expand_path('..', __dir__)
 Dir.chdir(APP_ROOT) do
-  begin
-    exec "yarnpkg", *ARGV
-  rescue Errno::ENOENT
+  yarn = ENV["PATH"].split(File::PATH_SEPARATOR).
+    select { |dir| File.expand_path(dir) != __dir__ }.
+    product(["yarn", "yarn.cmd", "yarn.ps1", "yarnpkg"]).
+    map { |dir, file| File.expand_path(file, dir) }.
+    find { |file| File.executable?(file) }
+
+  if yarn
+    exec yarn, *ARGV
+  else
     $stderr.puts "Yarn executable was not detected in the system."
     $stderr.puts "Download Yarn at https://yarnpkg.com/en/docs/install"
     exit 1