feat: added prop placeholderClass

Author: mfuu

package.json

@@ -1,6 +1,6 @@
 {
   "name": "vue-virtual-draglist",
-  "version": "3.3.2",
+  "version": "3.3.3",
   "description": "A virtual scrolling list component that can be sorted by dragging, support vue3",
   "main": "dist/virtual-drag-list.min.js",
   "types": "types/index.d.ts",
@@ -10,9 +10,10 @@
   ],
   "scripts": {
     "lint": "eslint --fix src --ext .js",
-    "test": "echo \"Error: no test specified\" && exit 1",
-    "build:dev": "cross-env mode=development rollup -c rollup.config.js -w",
-    "build": "cross-env mode=production rollup -c rollup.config.js"
+    "build": "cross-env mode=production rollup -c rollup.config.js",
+    "docs:dev": "vitepress dev docs",
+    "docs:build": "vitepress build docs",
+    "docs:preview": "vitepress preview docs"
   },
   "repository": {
     "type": "git",
@@ -40,7 +41,7 @@
   },
   "homepage": "https://github.com/mfuu/vue3-virtual-drag-list#readme",
   "dependencies": {
-    "sortable-dnd": "latest"
+    "sortable-dnd": "^0.6.19"
   },
   "devDependencies": {
     "@babel/core": "^7.15.0",
@@ -51,12 +52,16 @@
     "@rollup/plugin-node-resolve": "^13.3.0",
     "@rollup/plugin-terser": "^0.4.4",
     "@rollup/plugin-typescript": "^8.3.3",
+    "@vitepress-demo-preview/component": "^2.3.2",
+    "@vitepress-demo-preview/plugin": "^1.2.3",
     "cross-env": "^7.0.3",
     "lint-staged": "^11.1.2",
+    "mockjs": "^1.1.0",
     "prettier": "^2.3.2",
     "rollup": "^2.56.2",
     "rollup-plugin-dts": "^4.2.3",
     "typescript": "^4.3.5",
+    "vitepress": "^1.4.1",
     "vue": "^3.2.2"
   }
 }