Remove hardcoded DOCKER_TAG

Closes #732

Author: Keats

Dockerfile

@@ -3,7 +3,6 @@ RUN install_packages python-pip curl tar python-setuptools rsync binutils
 RUN pip install dockerize
 RUN mkdir -p /workdir
 WORKDIR /workdir
-ENV DOCKER_TAG v0.7.0
 RUN curl -L https://github.com/getzola/zola/releases/download/$DOCKER_TAG/zola-$DOCKER_TAG-x86_64-unknown-linux-gnu.tar.gz | tar xz
 RUN mv zola /usr/bin
 RUN dockerize -n  -o /workdir  /usr/bin/zola