dockerfile: change jdk8 to jdk 11

Dockerfile

-FROM openjdk:8-jdk-alpine
+FROM openjdk:11-jdk-slim
 ARG JAR_FILE=target/*.jar
 COPY ${JAR_FILE} app.jar
-ENTRYPOINT ["java","-jar","/app.jar"]
\ No newline at end of file
+ENTRYPOINT ["java","-jar","/app.jar"]