devbase:
 FROM: phusion/baseimage
 command: |
  RUN apt-get -y update && apt-get -y install \
      build-essential \
   && mkdir /opt

airline_data:
 requires:
  - devbase
 build_directory: sample_data/airline_data
 command: |
  ADD AirlinePassengers.csv

plant_data:
 requires:
 - devbase
 build_directory: sample_data/plant_growth
 command: |
  ADD Puromycin.csv

python_image:
 requires:
  - devbase
 command: |
  RUN apt-get -y update \
  && apt-get install -y \
    python \
    python-dev \
    python-pip \
    liblapack-dev \
    libblas-dev \
    gfortran \
    libpng12-dev \
  && pip install \
    numpy \
    scipy \
    pandas \
  && apt-get clean && rm -rf /var/lib/apt/lists/*

data_science:
 requires:
  - python_image
  - airline_data
  - plant_data

data_image:
 FROM: phusion/baseimage
 build: RUN mkdir /data

devbase:
 FROM: phusion/baseimage
 build: |
  RUN apt-get -y update && apt-get -y install \
      build-essential \
   && mkdir -p /opt

airline_data:
 requires:
  - data_image
 build_directory: sample_data/airline_data
 build: |
  ADD AirlinePassengers.csv /data

plant_data:
 requires:
 - data_image
 build_directory: sample_data/plant_growth
 build: |
  ADD Puromycin.csv /data

python_image:
 requires:
  - devbase
 build: |
  RUN apt-get -y update \
  && apt-get install -y \
    python \
    python-dev \
    python-pip \
    liblapack-dev \
    libblas-dev \
    gfortran \
    libpng12-dev \
  && pip install \
    numpy \
    scipy \
    pandas \
  && apt-get clean && rm -rf /var/lib/apt/lists/*

data_science:
 requires:
  - python_image
  - airline_data
  - plant_data

Change 'command' keyword to 'build'
Change 'command' keyword to 'build'
