Updating the docker test file to work with python 3.6

Author: JeffAshton

Dockerfile-test

@@ -1,9 +1,9 @@
 FROM ubuntu:latest
 
 RUN apt-get update && apt-get upgrade -y
-RUN apt-get -y install build-essential python-setuptools python2.7 python2.7-dev libssl-dev git tox python-pip
+RUN apt-get -y install build-essential python3.6 python3.6-dev python3-pip libssl-dev git
 
 WORKDIR /home/elastalert
 
 ADD requirements*.txt ./
-RUN pip install -r requirements-dev.txt
+RUN pip3 install -r requirements-dev.txt