Merge branch 'issue-267' into vorburger

* issue-267:
  add missing :java8 to FROM itzg/minecraft-server in Dockerfile (fixes OASIS-learn-study#267)

Author: vorburger

Dockerfile

@@ -5,7 +5,7 @@ COPY . /project
 WORKDIR /project
 RUN ./gradlew build -x test
 
-FROM itzg/minecraft-server
+FROM itzg/minecraft-server:java8
 COPY --from=build /project/web/build/libs/*-all.jar /data/mods/
 
 ENV EULA=TRUE