anchor.diff:      add-apt-repository 'deb http://cran.rstudio.com/bin/linux/ubuntu trusty/' && \
       add-apt-repository ppa:git-core/ppa && \
       add-apt-repository ppa:pi-rho/dev && \
  -    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9 &&
  +    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9 && \
       apt-get update && apt-get install -y -q curl && \
       (curl -sL https://deb.nodesource.com/setup_4.x | sudo -E bash -)
   
  
positive.code: 
  # Install RVM, Ruby, and gist.
  
  RUN gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 &&
      (curl -sSL https://get.rvm.io | bash -s stable --ruby) &&
      bash -c "(. /usr/local/rvm/scripts/rvm && gem install gist)"
  
  # Install npm packages.
  
negative.code: 
  WORKDIR /
  RUN /bin/rm -rf /tmp/build
  