Upgrade to Open JDK 11. (#56)

Specify particular version of docker client's API.

Dockerfile

@@ -1,9 +1,12 @@
+ARG docker_version=19.03
+
 FROM folioci/alpine-jre-openjdk11:latest
 
 ENV VERTICLE_FILE edge-oai-pmh-fat.jar
 
 # Set the location of the verticles
 ENV VERTICLE_HOME /usr/verticles
+ENV DOCKER_API_VERSION=1.39
 
 # Copy your fat jar to the container
 COPY target/${VERTICLE_FILE} ${VERTICLE_HOME}/${VERTICLE_FILE}