Update package.json

Windows packaging cannot generate root directory sotrable.js problem fit

Author: jombLiu

package.json

@@ -19,7 +19,7 @@
 	"main": "./Sortable.min.js",
 	"module": "modular/sortable.esm.js",
 	"scripts": {
-		"build:umd": "NODE_ENV=umd rollup -c ./scripts/umd-build.js",
+		"build:umd": "set NODE_ENV=umd&& rollup -c ./scripts/umd-build.js",
 		"build:umd:watch": "set NODE_ENV=umd&& rollup -w -c ./scripts/umd-build.js",
 		"build:es": "set NODE_ENV=es&& rollup -c ./scripts/esm-build.js",
 		"build:es:watch": "set NODE_ENV=es&& rollup -w -c ./scripts/esm-build.js",