Upgrade base docker image naar 11-jre-alpine

Dockerfile

@@ -1,4 +1,4 @@
-FROM openjdk:8-jre-alpine
+FROM openjdk:11-jre-alpine
 EXPOSE 8080
 ADD target/puzzeltocht-1.0-SNAPSHOT.jar /
 CMD ["java", "-jar", "puzzeltocht-1.0-SNAPSHOT.jar"]