Issue #2: Dockerfile: install of dependencies in Docker

The Dockerfile was incorrectly setting the list of
dependencies. It should be from the requirements.txt

This time the image is correctly built with the
dependencies, if new ones are added.

Dockerfile

@@ -1,8 +1,10 @@
 FROM marcellodesales/github-enterprise-prereceive-hook-base
 MAINTAINER Marcello_deSales@intuit.com
 
-RUN \
-  apk add --no-cache py-pip && \
-  pip install yamllint pyyaml pyjavaproperties
+RUN apk add --no-cache py-pip
 
-ADD ./validate_config_files.py /home/git/test.git/hooks/pre-receive
+COPY requirements.txt requirements.txt
+
+RUN pip2 install -r requirements.txt
+
+COPY ./validate_config_files.py /home/git/test.git/hooks/pre-receive