issue on app docker file

Hello, 
Before executing the docker build require to add this line to app docker file
`RUN easy_install distribute`
Then the docker file for application most update as blow 
`FROM python:2.7
WORKDIR /usr/src/app
COPY requirements.txt ./
RUN easy_install distribute
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
CMD [ "python", "tracker.py" ]`