UNOMI-661: Updated base image to openjdk 11 (#495)

diff --git a/docker/src/main/docker/Dockerfile b/docker/src/main/docker/Dockerfile
index 76a33a7..72b6e0d 100644
--- a/docker/src/main/docker/Dockerfile
+++ b/docker/src/main/docker/Dockerfile
@@ -15,7 +15,7 @@
 # limitations under the License.
 ################################################################################
 
-FROM openjdk:8-jre
+FROM openjdk:11-jre
 
 # Unomi environment variables
 ENV UNOMI_HOME /opt/apache-unomi