updated root check command

alpine/alpine-resize-disk.sh

@@ -1,8 +1,8 @@
 #!/bin/ash
 
-if ! [ $(id -u) = 0 ]; then
+if [[ ! $(id -u) = 0 ]]; then
     echo "Please run as root!"
-exit 1
+    exit 1
 fi
 
 apk add --no-cache cfdisk e2fsprogs-extra