anchor.diff:  
   # Ubuntu's python-pip throws exception with requests lib
   # see https://bugs.launchpad.net/ubuntu/+source/python-pip/+bug/1306991
  -RUN wget https://bootstrap.pypa.io/get-pip.py && \
  +RUN wget -q https://bootstrap.pypa.io/get-pip.py && \
       python get-pip.py && \
       rm get-pip.py
   
  
positive.code: ENV NODE_ARCHIVE=$NODE_DIR.tar.xz
  ENV PATH=/opt/node/bin:$PATH
  
  RUN apt-get -y update && apt-get install -y \
          firefox \
          gcc \
          libyaml-dev \
  
negative.code: # Install Google Chrome
  RUN wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add -
  RUN echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list
  RUN apt-get update -q -yy && apt-get install -yy google-chrome-stable
  RUN google-chrome --version
  
  # Install node.js; use most recent version to have access to latest features
  WORKDIR /opt
  RUN wget -q https://nodejs.org/dist/v6.2.0/$NODE_ARCHIVE && \
      tar xJf $NODE_ARCHIVE && \
      ln -s /opt/$NODE_DIR /opt/node && \
      rm $NODE_ARCHIVE
  