install.rb in jsbundling-rails-0.2.2

- old
+ new

@@ -7,6 +7,7 @@
 
 if (`npx -v`.to_f < 7.1 rescue "Missing")
   say %(Add "scripts": { "build": "#{build_script}" } to your package.json), :green
 else
   run %(npm set-script build "#{build_script}")
+  run %(yarn build)
 end