fix using importmap

[d6rkaiz]

fix: #5

• Bundled with this Gem is requestjs.js, not request.js.
  • https://github.com/rails/requestjs-rails/blob/main/app/assets/javascripts/requestjs.js
• Did not work to: "rails-requestjs", but it worked to: "requestjs.js"

[marcelolx]

Thanks @d6rkaiz!