Update dependency openjdk to v11.0.15 (#314)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

Dockerfile

@@ -22,7 +22,7 @@ WORKDIR /home/gradle/src
 
 RUN ./gradlew build --info
 
-FROM openjdk:11.0.14-jre-slim
+FROM openjdk:11.0.15-jre-slim
 
 RUN mkdir -p /app/releases
 RUN mkdir -p /app/configs