Support yarn as alternative to npm

Author: ntkme

ext/sass/.gitignore

@@ -8,3 +8,4 @@
 /node_modules/
 /protoc.exe
 /ruby/
+/yarn.lock

ext/sass/Rakefile

@@ -10,7 +10,7 @@ end
 
 CLEAN.include %w[protoc.exe ruby *.proto *.tar.gz *.zip]
 
-CLOBBER.include %w[dart-sass cli.rb embedded_sass_pb.rb node_modules package-lock.json]
+CLOBBER.include %w[dart-sass cli.rb embedded_sass_pb.rb node_modules package-lock.json yarn.lock]
 
 file 'protoc.exe' do |t|
   fetch(ENV.fetch('PROTOC_BIN') { SassConfig.default_protoc }, t.name)
@@ -30,6 +30,8 @@ rescue StandardError
 end
 
 file 'node_modules/sass' do
+  sh 'yarn', 'install'
+rescue RuntimeError
   sh 'npm', 'install'
 end