feat(minecraft-server): update spigot plugins using /plugins if newer

Deep copy and *.jar files in /plugins and update the corresponding files
in the /data/plugins dir.

minecraft-server/Dockerfile

@@ -14,6 +14,7 @@ RUN apk add --no-cache -U \
           jq \
           mysql-client \
           tzdata \
+          rsync \
           python python-dev py2-pip
 
 RUN pip install mcstatus

minecraft-server/start-minecraftFinalSetup

@@ -54,8 +54,12 @@ done
 
 if [ "$TYPE" = "SPIGOT" ]; then
   if [ -d /plugins ]; then
+    # Copy all of the plugins directory first to include initial configs
     echo Copying any Bukkit plugins over
     cp -r /plugins /data
+    # Copy plugins over using rsync to allow deeply nested updates of plugins
+    # only updates files if the source file is newer and print updated files
+    rsync -a --out-format="update:%f:Last Modified %M" --prune-empty-dirs --include '*/' --include '*.txt' --exclude '*' --update /plugins /data/plugins
   fi
 fi