###报错:###
/home/daniel/.rvm/gems/ruby-2.0.0-p247@rails4/gems/execjs-2.0.2/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
###解决:### sudo apt-get install nodejs