mc: avoid usermod when UID matches current user ID

minecraft-server/start

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 if [ $(id -u) = 0 ]; then
-  if [[ -v UID ]]; then
+  if [[ -v UID && $UID != $(id -u) ]]; then
     usermod -u $UID minecraft
   fi
   if [[ -v GID ]]; then