install nodejs/npm on workers

for Scala.js. requested by @sjrd at scala/community-build#276

Author: SethTisue

recipes/_worker-init-debian.rb

@@ -9,6 +9,8 @@
 
 include_recipe "apt" # do apt-get update
 
+include_recipe "nodejs"  # for Scala.js
+
 include_recipe "scala-jenkins-infra::_java_packages"
 
 # NOTE: MUST BE LAST -- it selects the chef-configured jdk (the above packages install openjdk 7 & 8, but we want something else)