Switch to openjdk-latest and don't copy server.jar

No longer copying server.jar since we expected it to exist already.
Build using the latest version of openjdk.

Dockerfile

@@ -1,6 +1,4 @@
-FROM openjdk:8-slim
-
-COPY server.jar /server.jar
+FROM openjdk:latest
 
 RUN groupadd -r minecraft -g 2000
 RUN useradd --no-log-init minecraft -u 2000 -g 2000 -m
@@ -9,4 +7,4 @@ RUN chown -R minecraft:minecraft .
 
 USER minecraft
 # Copy files only if they don't yet exist (server.jar, server.properties, etc) and start the server
-CMD java -Xmx"$MAX_RAM"G -Xms"$MIN_RAM"G -jar /server.jar nogui
+CMD java -Xmx"$MAX_RAM"G -Xms"$MIN_RAM"G -jar ./server.jar nogui