install unzip command on all images

Author: Paul van Leeuwen

Dockerfile

@@ -1,6 +1,6 @@
    RUN apt-get update && \
-       `# composer uses git` \
-       apt-get install -y git && \
+       `# composer uses git and unzip` \
+       apt-get install -y git unzip && \
        apt-get autoremove -y && \
        rm -rf /var/lib/apt/lists/*
   COPY composer.phar /usr/local/bin/composer