Do not download dockerize, use docker caches - fixes #136 (#148)

docker/Dockerfile

@@ -1,14 +1,19 @@
 FROM openjdk:8-jre-alpine
 VOLUME /tmp
-ARG DOCKERIZE_VERSION
-ARG ARTIFACT_NAME
-ARG EXPOSED_PORT
-ENV SPRING_PROFILES_ACTIVE docker
 
-ADD https://github.com/jwilder/dockerize/releases/download/${DOCKERIZE_VERSION}/dockerize-alpine-linux-amd64-${DOCKERIZE_VERSION}.tar.gz dockerize.tar.gz
+# Download dockerize and cache that layer
+ARG DOCKERIZE_VERSION
+RUN wget -O dockerize.tar.gz https://github.com/jwilder/dockerize/releases/download/${DOCKERIZE_VERSION}/dockerize-alpine-linux-amd64-${DOCKERIZE_VERSION}.tar.gz
 RUN tar xzf dockerize.tar.gz
 RUN chmod +x dockerize
+
+# This is the first layer that won't be cached
+ARG ARTIFACT_NAME
 ADD ${ARTIFACT_NAME}.jar /app.jar
-RUN touch /app.jar
+
+ARG EXPOSED_PORT
 EXPOSE ${EXPOSED_PORT}
+
+ENV SPRING_PROFILES_ACTIVE docker
+
 ENTRYPOINT ["java", "-XX:+UnlockExperimentalVMOptions", "-XX:+UseCGroupMemoryLimitForHeap", "-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]