fix reference error in the upload script

Author: cometkim

packages/playground/scripts/upload_bundle.sh

@@ -5,7 +5,7 @@
 # This script requires `curl` / `openssl` to be installed.
 
 SCRIPT_PATH=${BASH_SOURCE[0]}
-SCRIPT_DIR=$(dirname "$(dirname "$current_script_path")")
+SCRIPT_DIR=$(dirname "$(dirname "$SCRIPT_PATH")")
 
 # Get the actual version from the compiled playground bundle
 VERSION=$(cd $SCRIPT_DIR; node -e 'require("./compiler.js"); console.log(rescript_compiler.make().rescript.version)')