Remove zip dependency and replace with unzip equivalent (#354)

diff --git a/Dockerfile b/Dockerfile
index 0502845..90a733d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,6 @@
 FROM openjdk:8-jdk
 
-RUN apt-get update && apt-get install -y git curl zip && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y git curl && rm -rf /var/lib/apt/lists/*
 
 ENV JENKINS_HOME /var/jenkins_home
 ENV JENKINS_SLAVE_AGENT_PORT 50000