尝试加载宝石“uglifier”时出错。-沃克

我在将应用程序配置为用户wercker时遇到问题。我的沃克。yml看起来像这样:

box: ruby
services:
  - postgres
build:
    steps:
        - script:
            name: Nokogiri fix
            code: bundle config build.nokogiri --use-system-libraries
        - bundle-install
        - rails-database-yml
        - script:
            name: Set up db
            code: bundle exec rake db:schema:load RAILS_ENV=test
        - script:
            name: rspec
            code: bundle exec rspec

运行构建时失败,错误如下:

rake aborted!
Bundler::GemRequireError: There was an error while trying to load the gem 'uglifier'.
/pipeline/source/config/application.rb:7:in `<top (required)>'
/pipeline/source/Rakefile:4:in `require'
/pipeline/source/Rakefile:4:in `<top (required)>'
ExecJS::RuntimeUnavailable: Could not find a JavaScript runtime. See https://github.com/rails/execjs for a list of available runtimes.
/pipeline/cache/bundle-install/ruby/2.3.0/gems/execjs-2.6.0/lib/execjs/runtimes.rb:48:in `autodetect'
/pipeline/cache/bundle-install/ruby/2.3.0/gems/execjs-2.6.0/lib/execjs.rb:5:in `<module:ExecJS>'
/pipeline/cache/bundle-install/ruby/2.3.0/gems/execjs-2.6.0/lib/execjs.rb:4:in `<top (required)>'
/pipeline/cache/bundle-install/ruby/2.3.0/gems/uglifier-2.7.2/lib/uglifier.rb:3:in `require'
/pipeline/cache/bundle-install/ruby/2.3.0/gems/uglifier-2.7.2/lib/uglifier.rb:3:in `<top (required)>'
/pipeline/source/config/application.rb:7:in `<top (required)>'
/pipeline/source/Rakefile:4:in `require'
/pipeline/source/Rakefile:4:in `<top (required)>'
(See full trace by running task with --trace

我认为我需要在wercker上安装nodejs,但问题是我如何做到这一点?