upgrade docker images versions

Dockerfile

-FROM maven:3.2.5-jdk-8-onbuild
+FROM maven:3.3.9-jdk-8-onbuild
 VOLUME /var/lib/jetty/webapps
 CMD cp /usr/src/app/elevator-server/target/*.war /var/lib/jetty/webapps/root.war

README.md

@@ -81,7 +81,7 @@ At this point, the Maven build of code-elevator will be managed, and the result
 volume managed by the container. The only remaining thing is to execute a Jetty container allowing to run our
 application:
 
-- `docker run --detach --publish 8080:8080 --volumes-from code-elevator-container jetty:9.2.9-jre8`
+- `docker run --detach --publish 8080:8080 --volumes-from code-elevator-container jetty:9.3.10-jre8`
 
 That's all! The server is now up and running in a Docker container!
 

run.sh

@@ -2,4 +2,4 @@
 
 docker run --name code-elevator-container code-elevator
 #replace 9000 by whatever port you want to expose ie 80
-docker run --detach --publish 9000:8080 --volumes-from code-elevator-container jetty:9.2.9-jre8
+docker run --detach --publish 9000:8080 --volumes-from code-elevator-container jetty:9.3.10-jre8